Water and Waste Water Treatment Research in Mexico and Its Occurrence in Relation to Sustainable Development Goal 6

Abstract

In Mexico, 95% of the population has access to drinking water sources, but only about 65% of domestic waste water is treated to safe levels. This study analyzes forty years of Mexican scientific production on water and waste water treatment through a bibliometric and conceptual approach, evaluating its contribution Sustainable Development Goal (SDG) 6. The analysis identified three major research clusters: (1) biological processes for water treatment, (2) development and optimization of physical–chemical processes, and (3) water quality and management. These themes reflect the evolution of biological approaches for identifying and removing organic contaminants, the application of advanced techniques for improving water quality, and the promotion of sustainable water use. The study also highlights the growing attention to emerging contaminants, nanotechnology, integrated water resource management, and persistent challenges in sanitation. With respect to SDG 6, Mexican research has mainly focused on targets 6.1 (universal and equitable access to drinking water), 6.3 (water quality), and 6.5 (water resources management), while targets 6.2 (sanitation), 6.a (international cooperation), and 6.b (community participation) remain underrepresented compared with the international benchmarks, where the research trend is on water management, resources, and the water–food–energy nexus. Finally, the findings also show synergies with SDGs 11 (sustainable cities and communities), 9 (industry, innovation, and infrastructure), and 3 (good health and well-being), although gaps persist in addressing equitable access to water and society participation.

1. Introduction

Human survival is intrinsically linked to the natural resources that the Earth provides, including water. Throughout human history, water has been decisive for the proper development of civilizations, and it is recognized as a key resource for all living beings. However, although 71% of the planet is covered by water [1], its availability is compromised daily by growing demand and pollution. Therefore, water scarcity is a global challenge affecting millions of people. According to the United Nations [2], about 2.2 billion people lack access to drinking water, and nearly 40% of the world’s population faces water. The situation is worsening in areas with drought conditions, where the lack of water affects health, food production, and economic development. In addition, climate change is also contributing to aggravating water scarcity, as it causes extreme weather events such as droughts and floods. Moreover, water demand is expected to increase due to world population growth [3].

Water is a complex issue in Mexico, with significant disparities in access to and availability of water resources [4], as occurs in rural areas, where the population distribution is wider, thereby affecting the establishment of the necessary infrastructure. Moreover, population expansion and most significant economic development have occurred in the northern part of the country, where water availability is lower.

The National Water Plan (PNH 2024–2030) presents a critical panorama where 35 million Mexicans lack access to water in quantity and quality, and 114 out of 653 aquifers are affected by overexploitation [5]. To address the issues, the PNH considers several priority commitments: first attending the prioritization of water access and the promotion of efficient use of water in industry processes. Other actions3 are to encourage the reuse of treated water, reduce distribution network leakages, and promote investment in robust water infrastructure.

1.1. Normativity in Mexico

In Mexico, Article 4 of the Mexican Constitution states, “Every person has the right to access, disposal and sanitation of water for personal and domestic consumption in a sufficient, healthy, acceptable and affordable manner” [6]. Therefore, the State must guarantee this right through the National Water Commission (CONAGUA), which is the agency in charge of the administration and monitoring of compliance with this mandate. Likewise, according to Article 115, CONAGUA distributes responsibility among municipal operating organizations, which must fulfill their duty to provide drinking water, sewage, and sanitation services [6].

In addition, the water regulatory framework is contained in the National Water Law (Ley de Aguas Nacionales [7]), which establishes how the use and exploitation of national waters will be carried out, including managing waste water discharges to national water bodies and granting or assigning water titles for consumptive and non-consumptive uses. In addition, several official regulations specific to water issues exist, including the maximum permissible limits for determining the quality of water for human consumption (sampling, transportation, surveillance, and control), for waste water discharges (surveillance, monitoring, depending on the disposal site), for the reuse of treated water, and for determining water availability, among others. However, even though the regulatory framework requires authorities to provide water resources and effluent sanitation, currently, the coverage of water for human consumption is 96.1%, where the urban population has greater coverage (98%) than the rural population (89%) [8].

1.2. Water and SDGs

According to the partial progress reported by CONAGUA in 2021 [8], conservation and restoration strategies for basins and aquifers were strengthened to improve the environmental services they provide, such as conserving natural wealth, protecting ecosystems, and ensuring water sources for the population. The volume of treated water increases annually; also, the number of treatment plants has been increased to protect Mexican water sources and promote the reuse of treated waste water. However, most waste water treatment systems are based on biological processes (activated sludge, 49.3%; dual, 23.4%; stabilization lagoons, 10.0%; aerated lagoons, 3.6%, among others) whose treatment efficiency is high, but which do not have any emission reduction or reutilization systems [9]. Such a situation is expected to stay the same since, in recent years, investment has yet to be made in the Waste Water Treatment Plant (WWTP) construction, only in their maintenance.

1.2.1. SDG 6: Clean Water and Sanitation

Despite significant scientific and technological advances, billions still do not have access to sanitation, safe water, and hygiene services. Achieving universal coverage requires a substantial increase in global progress rates: “sixfold for drinking water, fivefold for sanitation, and threefold for hygiene” [2]. Well-designed and implemented strategies and increased investment in innovation and capacity development are vital in impacting compliance with SDG 6. For example, in the area of waste water, there has been limited progress toward halving the proportion of untreated waste water by 2023. As of 2022, 58% of domestic waste water was treated. However, there are gaps in data on waste water and industrial sources, which poses a risk to more than 3000 million people living in territories without water quality information.

Furthermore, SDG 6, as stated on the SDGs United Nations page, has been integrated by several targets summarized in

Table 1. SDG 6 targets description [11].

Target	Description
6.1	By 2030, achieve universal and equitable access to safe and affordable drinking water for all.
6.2	By 2030, achieve access to adequate and equitable sanitation and hygiene for all and end open defecation, paying special attention to the needs of women and girls and those in vulnerable situations.
6.3	By 2030, improve water quality by reducing pollution, eliminating dumping and minimizing release of hazardous chemicals and materials, halving the proportion of untreated waste water and substantially increasing recycling and safe reuse globally.
6.4	By 2030, substantially increase water-use efficiency across all sectors and ensure sustainable withdrawals and supply of freshwater to address water scarcity and substantially reduce the number of people suffering from water scarcity.
6.5	By 2030, implement integrated water resources management at all levels, including through transboundary cooperation as appropriate.
6.6	By 2020, protect and restore water-related ecosystems, including mountains, forests, wetlands, rivers, aquifers and lakes.
6.a	By 2030, expand international cooperation and capacity-building support to developing countries in water- and sanitation-related activities and programs, including water harvesting, desalination, water efficiency, waste water treatment, recycling and reuse technologies.
6.b	Support and strengthen the participation of local communities in improving water and sanitation management.

. According to target 6.1, each country has over five years to reach 100% coverage. On the other hand, targets 6.2 and 6.3 mention access to sanitation and sewage to reduce water pollution, increasing the proportion of treated water that can be reused. However, in this aspect, Mexico is a little further behind since sewage coverage includes those systems that are connected to the public network, to a septic tank, and also those that have basic sanitation (floor drain, ravine, crack, river, lake or sea), which reaches 93.8% of the population. Yet, basic sanitation does not reduce the risk of contamination of water sources since it does not prevent the release of waste water into the environment. Therefore, according to the comprehensive index on SDG 6 (scale from 0 to 100) developed by Cai et al. [10], Mexico scores 45.2 on the Global baseline of Sustainable Development Goal 6, 40.6 on the Global baseline of Indicator 6.3.1 Proportion of safely treated household waste water, and 42.5 on the Proportion of population using safely managed drinking water services.

1.2.2. SDG 6 Link to Other SDGs

If the entire water cycle is analyzed, all the targets of SDG 6 are intertwined with the other SDGs, and they contribute to the three dimensions of sustainable development: social, economic, and environmental. To comply with SDG 6’s aims “Ensure availability and sustainable management of water and sanitation for all” [11] multiple synergies must be established.

Table A1. SDG 6 links to other goals [2,12,43,44,48].

SDG	Goal	Link to Other Goals	Dimensions
1	No poverty	Ensuring everyone can access basic services such as drinking water and new water treatment technologies helps reduce poverty in all dimensions.	S
2	Zero hunger	Adequate water treatment ensures agricultural productivity and the income of small-scale producers. Appropriately using treated water and rainwater collection can ensure sustainable food production. Finally, it promotes ending malnutrition by giving access to basic services and providing sufficient and safe food.	S, Ec, En
3	Good health and well-being	Reduction of diseases and deaths due to exposure to dangerous substances in water is influenced, especially maternal mortality and deaths in newborns and children under five years of age. The provision of quality health services depends on the existence of basic services.	S
4	Quality education	Access to basic services in educational institutions is required to ensure quality learning spaces. The absence of drinking water, handwashing facilities, and sanitation services in schools limits personal development at all levels.	S
5	Gender equality	Lack of water facilities dramatically impacts the lives of women and girls, as they disproportionately participate in water provisioning when unavailable.	S
6	Clean water and sanitation	-	S, Ec, En
7	Affordable and clean energy	Using waste water sludge can generate renewable energy (biogas) and reduce methane emissions. Capitalization of residues as byproducts increases the rate of renewable energy in systems and helps improve energy efficiency.	S, Ec, En
8	Decent work and economic growth	Establishing waste water recycling measures can provide additional sources of income to local authorities and their citizens. It is also an opportunity to incorporate informal sector personnel into the economy.	S, Ec, En
9	Industry, innovation, and infrastructure	Generating sustainable and resilient infrastructure promotes industrialization and continuous improvement by efficiently using resources in all processes.	Ec
10	Reduced inequalities	Providing quality basic services to the entire population encourages income growth for people experiencing poverty, promotes equity in opportunities, empowers, and promotes the inclusion of vulnerable sectors.	S, Ec
11	Sustainable cities and communities	Providing access to safe and affordable water impacts providing basic services and updating housing facilities. The generation of future emissions can be avoided by developing inclusive and sustainable water infrastructure in cities. Proper management of water resources also promotes universal access to urban green spaces.	S, Ec, En
12	Responsible consumption and production	Adequate water management impacts energy use and energy-related emissions, so achieving sustainable and efficient management promotes the consumption and production of water resources and using energy and land.	Ec, En
13	Climate action	Actions on waste water extraction, distribution, and processes reinforce resilience to natural disasters and risks related to climate change.	En
14	Life below water	Sustainable and restoration actions on water resources avoid nutrient loading and eutrophication of ecosystems. Poor management harms the health of communities, ecosystems, fisheries, and even tourism.	En
15	Life on land	Ensuring the conservation and restoration of ecosystems and their services encourages sustainable forest management. Deforestation can be avoided, which degrades the soil and promotes desertification and degradation of natural habitats.	En
16	Peace, justice, and strong institutions	Water infrastructure development depends on compliance with laws related to providing facilities that comply with quantity and quality regulations. The eradication of corruption ensures efficient resource use and equitable distribution among the entire population.	S
17	Partnership for the goals	The 17 SDGs have an extensive scope of application, so the direct links between some of them and SDG 6 are less explicit; however, they exist. The impact of water infrastructure is enormous, but a louder collective voice is still required in future local, national, and international meetings to support urgent collaborative actions.	S, Ec, En

Note: S = Social, Ec = Economic, En = Environmental.

lists the links between SDG 6 and the other SDGs and the dimensions to which they contribute.

According to the Water and sanitation interlinkages across the 2030 Agenda for Sustainable Development brief by the UN-Water, there are direct relationships between SDG 6 targets and most SDGs [12]. For example, the SDGs of the social dimension have a strong link with the targets related to supply, drainage, and hygiene (SDGs 1, 2, 3, and 4), with the water quality targets (SDGs 8, 5, and 10) and with the targets for improving the quality of water and waste water treatment and promoting efficient and sustainable use of water (SDGs 2, 7, 11, and 16). Whereas, in the economic dimension, there are solid links between the targets related to water supply (SDGs 8, 9, 11, and 12) since access to supply, drainage and hygiene services, and waste water treatment have a relevant impact on the health, education, and productivity of workers. In addition, in the economic dimension, a multidirectional relationship is observed with SDGs 7, 8, 9, and 12 since it is necessary to ensure both the provision of basic services and the maintenance of natural resources. Finally, there is a firm link between SDGs 12, 14, and 15 with the targets related to water quality, waste water management, and the improvement of aquatic and terrestrial ecosystems, which are associated with the environmental dimension.

1.3. Research Trends

Historically, water research has focused on issues related to making it suitable and safe for consumption. More recently, research trends have focused on removing contaminants in water for human consumption and waste water. Mexico has not been an exception. In recent years, research has focused on developing and implementing processes as diverse as electrochemistry, physicochemical processes, nanotechnology, and advanced oxidation, among others.

Nowadays, multidisciplinary research dominates the research panorama. Conservation of water resources has emerged as a key topic, and it has led to the integration of research groups that incorporate the technical and engineering parts and combine them with social input. This is relevant to the transfer, acceptance, and adaptation of technology that allows accessibility to the hydric resource in quantity and quality.

As a result, the former Mexican National Science Council (CONAHCYT, now Secihti), in the Special Program for Science, Technology, and Innovation (PECITI) (Programa Especial de Ciencia, Tecnología e Innovación 2021–2024, [13]) and the National Strategic Programs (PRONACES [14]) has stated that the right to science is linked to the enjoyment of other rights such as health, biodiversity, education, culture, and water, and has also urged to focus research on key national agendas. The PECITI proposes specific targets and actions to address the 14 SDGs and 29 goals of the United Nations 2030 Agenda. Key priorities include tackling and ensuring access to energy and water, quality education, healthy lives, food security, climate change, and gender equality. Similarly, solutions to national problems should be explored with the participation of the social, public, and private sectors and the scientific community. One of the main priorities is to ensure access to quality water. The PECITI establishes the specific action (3.2.9) of issuing calls for projects to conserve, manage, and restore freshwater systems. On the other hand, Water PRONACE encourages the formation of research groups to design and manage solutions to severe problems in the water cycle.

At the international level, meta-analyses and global SDG reviews reveal a broader and denser fabric of collaboration, with hotspots spanning water quality monitoring, sanitation and waste water management, governance, and cross-country policy alignment to SDG 6 targets [15,16,17]. Country level examples also illustrate how national agendas operationalize these goals. In Belgium for instance, mapping studies have linked research fronts to concrete SDG 6 priorities, monitoring indicators, and utilities’ challenges [18]. A multidisciplinary analysis by Ho et al. (2020) further demonstrated that, although high levels of access to drinking water and sanitation have been achieved, persistent issues remain regarding source contamination [18]. Their text-mining approach classified Belgian publications mainly under targets 6.3, 6.4, 6.5, and 6.6 with principal topics addressing water treatment, water pollution, water stress, climate change, and water resources modeling. Similar regional assessments, such as those conducted in the Gulf states, also highlight how water and climate research portfolios are being strategically tied to SDGs 6 and 13 [19].

On the other hand, countries classified as developed economies can invest in research and development of technologies to achieve water quality and management. In these regions, intersectoral participation is encouraged to ensure sustainable water management. Such is the case of water conditions in Pakistan, classified as a developing economy, where the authors conducted a holistic analysis of how the country could achieve SDG 6, involving a perspective on social, economic, environmental, and political aspects related to water management [20].

In Latin America, Macias-Quiroga et al. [21] conducted a regional bibliometrics analysis of advanced oxidation processes (AOPs) in waste water treatment and reported a sharp rise un AOP focused publications targeting emerging contaminants, alongside still fragmented collaboration networks that would benefit from stronger intraregional ties.

Against this backdrop, Mexican bibliometric contributions related to water have historically concentrated on sectoral themes, e.g., agriculture and water use [22], hydraulics [23] or forestry interfaces [24], and on specific application niches such as constructed wetlands with ornamental species or dam pollution assessments [25,26]. Network-oriented work in Mexico City further indicates that research outputs from water-access groups have had limited measurable impact on improving drinking-water access [27]. Compared with international benchmarks that align research portfolios with SDG indicator frameworks and leverage broad, multi-country collaborations [15,16,17], Mexico’s bibliometric landscape appears more thematically segmented and less explicitly tied to SDG 6 monitoring architecture.

Although earlier bibliometric studies have provided important insights into publication trends and thematic clusters, they have been largely descriptive and seldom assessed how national research portfolios connect to specific SDG 6 targets. In particular, underrepresented areas such sanitation, community participation, and international cooperation remain insufficiently addressed, and links to policy frameworks and technology transfer are rarely made. This study responds to that gap by systematically mapping Mexico’s water and waste water research to the SDG 6 targets and indicators, quantifying incidence and revealing where collaboration density and thematic alignment could most improve.

Thus, the present work contributes to the diagnosis and evaluation of the efforts of Mexican science in the scope of SDG 6 and its targets through research on water and waste water treatment issues. Forty years of literature published by authors working in Mexican institutions was analyzed in depth through a conceptual bibliometric analysis to achieve the following four objectives: (1) to determine the evolution of publications over time, as well as to identify relevant works, publication and funding sources and affiliation institutions; (2) to detect the topics that have been studied and how they relate to each other; (3) to understand how research themes have evolved and their level of importance and development in each analyzed period, and lastly (4) to establish the impact of this research on the SDG 6 targets and the other SDGs.

2. Materials and Methods

The objective of this study was to determine the contribution and evolution of Mexican research on water treatment, including waste water, to Sustainable Development Goal 6: Clean water and sanitation, and its targets. With this in mind, the first step was identifying the most appropriate combination of keywords to retrieve relevant publications. Thus, several combination tests were carried out in the Scopus database, a neutral-source citation and abstract database curated by independent subject matter experts who are recognized field leaders.

As a second stage, the conducted search was limited to the title, abstract, and keywords (authors’ and indexed keywords), including both words “water treatment” and “waste water treatment”, which were combined with words related to the water’s final use or quality, discarding “ground water” and greywater. However, the initially obtained databases included many documents about topics unrelated to our aim, and such an appearance was related to the inclusion of the indexed keywords. Therefore, the utilized search was limited to the two words “water treatment” and “waste water treatment” in the title, abstract, and keywords fields, together with other word combinations restricted to the title or author keywords fields.

The resulting query was introduced in Scopus, and it is TITLE-ABS-KEY (“water treatment” OR “waste water treatment”) OR TITLE ((water OR waste water) AND (drink* OR potable OR recycl* OR quality OR reuse)) OR AUTHKEY ((water OR waste water) AND (drink* OR potable OR recycl* OR quality OR reuse OR analy*)). Next, the resulting query was narrowed down, limiting the document type to articles, conference proceedings, reviews, book chapters, and books. Afterward, 2023 was established as the final year of publication, and Mexico was selected as the country of interest. The data collection and analysis methodology is shown in Figure 1.

Subsequently, the SDG 6 query was applied, which became the water query. Here, a final list of 3813 documents was obtained, which is the sample on which our study focuses. The water query incorporates terms considered for the classification of SDG 6, according to Bedard-Vallee et al. 2023 [28]. The exported data of the water query documents can be consulted in Listing S1.

Then, to assess the achievement of water treatment research in Mexico, target queries based on text mining proposed by Ho et al. were implemented in the water query for each of the eight SDG 6 targets [18]. Such queries were generated as scientific results often need to be determined, generating disconnections between the academic and implementation spheres.

Additionally, to find out how Mexican research on water treatment research impacts all the Sustainable Development Goals, the 16 queries corresponding to the other SDGs were applied to the water query. It is important to remark that the water query is already limited to the works that impact SDG 6.

Once all query results were exported, the data analysis stage was as follows. The water query results were examined through two complementary approaches: (1) Bibliometric Analysis—This stage assessed the publications’ temporal evolution, identified the institutions with the highest research output, highlighted the most influential funding sources, determined the leading publication sources, and the most cited documents. (2) Thematic Analysis—This included the generation of word clouds, identification of trending topics, construction of co-occurrence networks, and examination of thematic evolution across three time periods: 1984 to 2003, 2004 to 2013, and 2014 to 2023.

Moreover, the results from the target queries were used to quantify the cumulative number of publications associated with each SDG 6 target. Finally, the number of publications related to the remaining 16 SDGs was determined through a comprehensive analysis of the SDG queries results.

Finally, it is worth mentioning that the present analysis was limited to documents indexed in the Scopus database; therefore, some relevant documents might not be included. A valuable portion of Mexican research documents is published in local formal sources such as national journals, regional associations’ publications, and books. Also, there are important contributions within grey literature (project reports, governmental documents, regulations, and policy); therefore, they were consequently excluded in this study, as the present analysis was made on scholarly published documents. However, the authors are confident that the resulting document list is robust and complete enough to obtain reliable results.

3. Results and Discussion

This section aims to provide an overview of the contribution of researchers who do science in Mexico to technological development and innovation in water and waste water treatment, as well as to the advancement of Sustainable Development Goal 6. These results could be used as a reference to what has been done and how the trend of research in Mexico is developing, according to the United Nations 2030 Agenda.

Table 2. Bibliometric indicators.

Information	Data
Period	1984 to 2023
Sources	1040
Documents	3813
Documents per year	95.3
Average citations per document	25.08
References	167,744
Authors keywords/Index keywords	9020/19,795
Authors	11,242
Authors of single-authored documents	88
Documents per author	0.34
Authors per document	2.95
Co-authors per document	5.14
Collaboration Index	5.04

presents the most relevant bibliometric indicators of the analyzed sample. Although the search was carried out by limiting only the final date, the first document found on this topic dates back to 1984; therefore, the sample includes 40 years of documents.

Also of interest, most documents are in English (3555), and 308 are in Spanish. In addition, 2972 documents are articles, 290 reviews, 380 conference papers, 162 book chapters, and nine books. In addition, 30% of the publications are open-access (1145). The main areas within the documents are classified as (1) Environmental Science (2383), (2) Chemical Engineering (788), (3) Engineering (784), (4) Chemistry (660), and (5) Agricultural and Biological Sciences (510).

3.1. Publications over Time

Figure 2 shows the history of publications related to the topic of interest and how the publications have accumulated over the 40 years of this bibliometric analysis. During the first 20 years of publications, there was a maximum of 81 documents published annually (2005), while during the second half of the period, a maximum of 379 was reached (2022). Although the production of documents has been variable over the years, it is observed that there is a sustained upward trend, which has an exponential trend. However, 2023 had fewer documents than the year before, which had the highest production (2022).

3.2. Affiliation and Funding Institutions

Several institutions have generated the publications; the ten institutions showing the highest number of published documents are presented in

Table 3. Top ten affiliation institutions.

Rank	Affiliation	Affiliation ID	Documents
1	Universidad Nacional Autónoma de México (UNAM)	60032442	739
2	Instituto Politécnico Nacional (IPN)	60019176	346
3	Tecnológico de Monterrey (ITESM)	60007966	236
4	Universidad Autónoma del Estado de México (UAEMex)	60002281	223
5	Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional (CINVESTAV)	60017323	216
6	Universidad de Guanajuato (UGTO)	60033291	182
7	Instituto Mexicano de Tecnología del Agua (IMTA)	60017774	167
8	Universidad Autónoma de San Luis Potosí (UASLP)	60031335	143
9	Universidad de Guadalajara (UdeG)	60008943	129
10	Universidad Autónoma Metropolitana (UAM)—Unidad Iztapalapa	60028381	121

. The Scopus affiliation ID was added to the institutions for correct identification. The institution with the largest number of published documents is the Universidad Nacional Autónoma de México, with more than double the number of documents as the next institution, the Instituto Politécnico Nacional, Tecnológico de Monterrey appeared in third place, followed by the Universidad Autónoma del Estado de México, and the Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional. Notably, institutions between 6th and 10th place have over 100 published documents.

On the other hand, the information about the entities that finance the topic of water treatment was also analyzed, finding that the main financier of this research topic is the Consejo Nacional de Humanidades, Ciencias y Tecnologías CONAHCYT (formerly CONACYT), with more than 1000 documents that declare having been financed by this institution. The other founding sources are the Universidad Nacional Autónoma de México (UNAM), the Instituto Politécnico Nacional, and the Universidad de Guanajuato, respectively. Additionally, the Secretariats of Education, Environment, and Energy appear as research funders (Secretaría de Educación Pública SEP, Secretaría de Medio Ambiente y Recursos Naturales SEMARNAT, and Secretaría de Energía SENER).

Relevantly, it is observed that within the first fifteen financing entities, there are also international organizations, such as the European Commission, European Regional Development Fund, National Science Foundation (USA), Conselho Nacional de Desenvolvimento Científico e Tecnológico (Brazil), Ministerio de Economía y Competitividad (Spain) and the National Natural Science Foundation of China.

3.3. Sources and Documents

Table 4. Top ten publishing sources.

Rank	Source (ISSN; CiteScore 2023)	ND	H	TC	SYP
1	Water Science and Technology (0273-1223; 4.9)	202	32	3898	1991
2	Chemosphere (0045-6535; 15.8)	96	33	4459	1999
3	Revista Internacional de Contaminación Ambiental (0188-4999; 0.9)	94	11	441	1996
4	Science of the Total Environment (0048-9697; 17.6)	89	41	5358	2005
5	Water (Switzerland) (2073-4441; 5.8)	88	17	998	2012
6	Tecnología y Ciencias del Agua (0187-8336; 0.6)	75	8	228	2010
7	Environmental Science and Pollution Research (0944-1344; 8.7)	63	16	836	2007
8	Water Air and Soil Pollution (0049-6979; 4.5)	62	18	939	1985
9	Journal of Environmental Management (0301-4797; 13.7)	58	23	1810	2004
10	Bioresource Technology (0960-8524; 20.8)	49	34	5098	1997
10	Chemical Engineering Journal (1385-8947; 21.7)	49	28	3349	2001
10	Water Research (0043-1354; 20.8)	49	33	6728	1992

ISSN = International Standard Serial Number; ND = Number of documents; H = H index; TC = Total citations; SYP = Starting year of publication.

presents the top ten sources in which most documents were published. For each source, the number of documents (ND), H index (H), total citations (TC), and starting year of publication (SYP) were also determined to provide a comprehensive view of their impact.

The Water Science and Technology (formerly Progress in Water Technology) journal appears in the first place and is published by International Water Association Publications (IWA Publishing). This journal is classified within the area of Environmental Science in two subcategories (Water Science and Technology and Environmental Engineering). Chemosphere is the second journal in which water and waste water treatment topics are relevant. Elsevier publishes it and is classified into three areas (Medicine, Environmental Science, and Chemistry). The Revista Internacional de Contaminación Ambiental appears in third place, published by the Center for Atmospheric Sciences of the Universidad Nacional Autónoma de México, and is classified in Environmental Science.

In this list, two sources with the most published documents are Mexican: Revista Internacional de Contaminación Ambiental (third place) and Tecnología y Ciencias del Agua (sixth place); these journals date from 1996 and 2010, respectively.

Notably, the Journal of Hazardous Materials (ISSN: 0304-3894, CiteScore 25.4) does not appear in the previous table. This is relevant because it has the highest total citations in the entire database (7605) accumulated in 42 publications, with an H index of 33 (it began publishing in 2001).

In

Table 5. Most cited documents.

Rank	Reference	Title	Source	TC	FWCI	Type
1	[29]	Heterotrophic cultures of microalgae: Metabolism and potential products	Water Research	1255	9.87	re
2	[30]	Recent advances in removing phosphorus from waste water and its future use as fertilizer (1997–2003)	Water Research	1214	9.59	ar
3	[31]	Electrocoagulation (EC)—Science and applications	Journal of Hazardous Materials	1188	5.45	ar
4	[32]	Review paper on current technologies for decolourisation of textile waste waters: Perspectives for anaerobic biotechnology	Bioresource Technology	1148	6.95	re
5	[33]	Pharmaceuticals as emerging contaminants and their removal from water. A review	Chemosphere	1111	7.06	re
6	[34]	A review of chemical, electrochemical and biological methods for aqueous Cr(VI) reduction	Journal of Hazardous Materials	1094	5.59	re
7	[35]	Fundamentals, present and future perspectives of electrocoagulation	Journal of Hazardous Materials	1038	6.00	ar
8	[36]	Production of bioenergy and biochemicals from industrial and agricultural waste water	Trends in Biotechnology	848	5.78	re
9	[37]	Cr(VI) and Cr(III) removal from aqueous solution by raw and modified lignocellulosic materials: A review	Journal of Hazardous Materials	810	4.29	re
10	[38]	Molecular mechanisms of fluoride toxicity	Chemico-Biological Interactions	792	3.99	re

TC = Total citations; FWCI = Field-Weighted Citation Impact; re = review; ar = article.

, the most cited documents are listed, where it is observed that seven of the top ten are of the review article type.

The two most cited documents were published by the journal Water Research, and the third was published by the Journal of Hazardous Materials. The first seven articles have more than 1000 citations, whereas the first and second places have more than 1200. When analyzing the Field-Weighted Citation Impact (FWCI), which is a normalized citation indicator that relates the citations of an article with the expected citations according to the impact of citations weighted by field, it is observed that the documents listed are apparent leaders of the area studied, since they have high FWCI.

3.4. Thematic Analysis

The word cloud (Figure 3) is a visual representation of the most frequent terms contained in the documents of a database. In this case, it was generated from Bibliometrix version 4.1.4 (https://www.bibliometrix.org/) based on the 50 most frequent words contained in the: (a) title, (b) authors’ keywords, (c) index keywords, and (d) abstract from the analyzed documents. It should be noted that synonyms were established to merge matching terms. Also, the terms corresponding to the initial search (main query) were eliminated (i.e., water treatment, waste water treatment, among others) (See Listing S2).

As can be seen, the words water quality and drinking water appear in all four images, representing the frequency and relevance of the topic. This reflects the Mexican research trend around water quality monitoring and its assurance. In general, the rest of the words that appear in the clouds are more related to research on waste water treatment, with words such as waste water and anaerobic standing out. This suggests a broader research focus on water sanitation, a critical area in many countries such as Mexico, where eliminating contaminants from waste water is a growing priority involving both governmental efforts and the academic community.

The authors’ keywords word cloud contains the widest variety of terms. It includes words such as drinking water and waste water and its treatment, suggesting that multiple research topics should be addressed throughout the supply chain, including consumption and treatment of water resources. Water-related words include quality, waste water, and drinking water. This cloud also points to terms related to treatment processes, such as photodegradation, adsorbent, anaerobic, and electrocoagulation. These terms show the importance of technological and scientific advances in treatment methods. Finally, there are other words related to specific contaminants, such as arsenic, nitrate, fluoride, heavy metal, and emerging contaminants, which reflect the growing concern about the effects of these contaminants on water resources.

In summary, the word clouds show that the main water and waste water treatment research topics in Mexico are sanitation and water quality. In addition, although to a lesser extent, the clouds show that in Mexico, there is also research on emerging topics within the field of quality and drinking water.

3.4.1. Trend Topics

In Figure 4, each bubble represents a topic (term), and the bubble size is proportional to the topic frequency. The year in which the bubble appears represents the median, while the bar indicates the first and third quartiles of the distribution of occurrences. The three most frequent trending topics are reported each year. Based on the date of appearance of the topics, the trend and progress of the terminology can be observed.

Initially, the most frequently used terms were advanced primary treatment, UASB reactor, protozoa, and helminth eggs because the removal efficiency of pathogens in waste water treatment was a theme of concern. So, it can be observed that the most relevant water and waste water treatment topics in Mexico, when publications began, were related to the efficiency and stability of the process. Note that E. coli and stability are the terms that have been present in research in Mexico for the longest time, followed by terms like uasb reactor, biofilm, robust control, and model. Uasb reactor and biofilm are related to the use of microorganisms for the degradation of organic matter, that is, with waste water treatment. In the same way, terms such as robust control and model can be related to the stability of the treatment processes.

Terms such as circular bioeconomy, microplastics, graphene, and emerging contaminants started appearing after 2020. Such a development reflects the technological advances in detecting contaminants at low concentrations in water and the relevance that this has triggered in the search for treatment strategies with a circular economy approach.

The publication timeline in Scopus shows that at the beginning of water and waste water treatment research in Mexico, the central themes were stabilizing, and controlling the process. Later, the themes focused on advanced processes or removing a specific contaminant, nitrates, arsenic, and azo dye, among others. Recently, the most relevant themes included nanotechnology, advanced oxidation processes, microplastics, or circular economy. The relevance of themes such as waste water or water quality stands out, as they are the most mentioned of all time.

Finally, terms such as heterogeneous photo-Fenton, methyl orange, and circular bioeconomy are concepts that began to appear recurrently in the last two years and that are somehow related to each other, given the effectiveness that advanced oxidation processes have demonstrated for the degradation of dyes so that water can be reused.

3.4.2. Co-Occurrence Network

Word analysis helps identify the main topics based on how frequently they occur and how they are related. In a co-occurrence analysis, the premise is that the terms’ interaction in a document allows the description of its content [39]. Therefore, two documents are more similar as they have more terms in common and probably share the same research field. A network map is a visualization technique to show these interactions between documents, where each circle represents a term or topic, and its occurrence’s frequency determines the size of the label and the circle; the larger the label and the circle, the higher the occurrence of the word.

Figure 5 shows the co-occurrence network generated using the Bibliometrix R package version 4.1.4 and visualized in VOSviewer version 1.6.20, considering the 100 most frequent words. Three word clusters are identified, each represented by a distinct color. The width of the connecting lines between circles indicates the strength of their co-occurrence. The words in the red cluster relate to the biological part of water treatment strategies. The green cluster refers to treatment processes in general, mainly physicochemical, which can be applied to drinking or waste water treatment. Finally, the blue cluster includes words related to water management, water sources, and water uses, among others. The full list of words contained in each cluster may be found in Listing S3 (Additional Information).

In the red cluster, the five most important terms are anaerobic, activated sludge, microalgae, nutrient recovery, and biodegradability. These five words apply to the biological aspects of water treatment, where most processes are carried out with activated sludge, either anaerobic or aerobic, to remove nutrients. This is related to the biodegradability of organic matter, and in some cases, microalgae can be involved as part of the microbial consortiums.

On the other hand, waste water treatment, waste water, adsorbent, water treatment, and photodegradation were the most frequently found words in the green cluster. In this case, adsorption with different adsorbents and photodegradation were physicochemical processes applied to water and waste water treatment.

Finally, in the blue cluster, words like water quality, drinking water, arsenic, Mexico, and groundwater were the most important. All of them are related to the terms used in the water for human consumption theme. For example, arsenic is an element of great interest, commonly found in Mexico’s aquifers (groundwater).

3.4.3. Thematic Evolution (1984 to 2003)—(2004 to 2013)—(2014 to 2023)

The thematic evolution is established from a “co-word” analysis, allowing the detection of relevant topics in a given period through a co-occurrence analysis. Such analysis is followed by a grouping process to establish subgroups of closely related words that can be interpreted as specific research themes or clusters [39].

Once the clusters are identified, a strategic diagram consisting of four thematic quadrants can be obtained [40]. The four quadrants are (1) the upper right, which shows the driving themes: high importance and high level of development and which are externally related to concepts of other themes; (2) the upper left, which contains the niche themes: well-structured internally so they are very specialized themes, but they are poorly related to concepts of external themes; (3) the lower left, representing marginal and underdeveloped themes: they may be emerging or in the process of disappearing, and lastly, (4) the lower right, which contains basic themes: this is important but underdeveloped themes.

Figure 6 shows the strategic diagrams for each period; the words that make up the clusters can be found in Listing S3. The analysis was carried out using Bibliometrix, with the “walktrap” clustering algorithm [41], where a minimum of five documents per thousand was considered for the cluster formation.

The strategic diagrams in Figure 6a show that in the first research period (1984 to 2003), the driving themes (upper right quadrant) were diverse or miscellaneous. Here, the waste water and water quality clusters stand out for their density. However, the waste water cluster remains a driving theme for the second period (2004 to 2013) (Figure 6b). Here, the waste water treatment cluster appears, and the remaining clusters from the previous period disappear or change quadrant. For example, the sbr cluster moves from the upper right quadrant in the first period to the lower right quadrant as a passive and poorly developed theme in the second period. Also, the coagulant cluster emerges among the driving themes within the second period, although with less density.

For the third period (2014 to 2023), in Figure 6c, the motor themes disappear, and the water quality cluster is positioned at the center of the quadrants with a medium density. Among the niche themes (upper left quadrant) during the three periods, the clusters varied from each other; namely, the specialized themes changed significantly over time. In the lower left quadrant, the less developed themes are found. The sorption cluster appears in this quadrant in the first period, and then it evolves towards the basic themes’ quadrant in the third period, similarly to the adsorbent cluster. The waste water treatment cluster also appears among the basic themes of this study period, which in the previous period was among the motor themes. Finally, it is observed that no marginal themes appeared in the third period, and only two niche themes were formed.

On the other hand, it is possible to map the thematic evolution of research between two consecutive subperiods by finding and connecting their specific themes (clusters). A theme in subperiod A is considered to have evolved into a theme of the following subperiod B if they share keywords since these words form a thematic link that can be weighed by the inclusion index and represented on the map by the width of the links [42]. Therefore, the inclusion index will be equal to 1, if all words of the theme in subperiod A are contained in the theme in subperiod B.

Figure 7, obtained with data from Bibliometrix analysis, represents the thematic evolution of the themes related to water research in Mexico since the first Scopus publication in 1984. In the first twenty years of research, a greater variety of relevant or recurrent terms was narrowed down or grouped according to the research trend.

In the first period (1984 to 2003), the waste water cluster included concepts mostly related to biological water treatment, including terms such as anaerobic, activated sludge, aerobic, and bacterial communities, among others. Notably, the subjects in this cluster are focused on topics related to waste water treatment because, at that time, understanding and improving the treatment systems and contributing to the research were considered relevant for ecosystems and health preservation. Due to the findings, the waste water cluster diversifies by the second period (2004 to 2013) into clusters that include waste water treatment, drinking water, aerobic (treatment systems), and coagulant as main themes. Finally, the waste water cluster is incorporated into water quality, waste water treatment, and adsorbent clusters for the third period (2014 to 2023).

Clusters such as nitrogen, ozone, and municipal waste water, separated in the first period, are completely included in the waste water treatment cluster in the second period. Likewise, the second period incorporates terms such as arsenic, water treatment, sorption, and drinking water into the drinking water cluster.

Therefore, in the second period, nine clusters can be observed, including waste water treatment, waste water, drinking water, water quality, climate change, optimization, sbr, coagulant, and anaerobic. The relevance of two of these clusters is evident as they remain in the third period, like water quality and waste water treatment. During this period, the importance of water treatment, either for human consumption or waste water, is observed. Through continued research, analytical methods are developed and improved, and the scope of water quality parameters for preserving water sources and the population’s health is broadened.

Four clusters are highlighted in the third period, which contain those developed in the first two periods. For example, water quality is formed by related themes, such as waste water, drinking water, water quality, climate change, and optimization. The emergence of the adsorbent cluster, which is integrated, in order of contribution, by climate change, drinking water, waste water treatment, sbr, waste water, and water quality clusters, is noteworthy. This could be due to technological development, which includes the capacity to modify materials by reducing their size (nanomaterials) or generating complex composite materials; this cluster’s research, application, and relevance have been boosted. Furthermore, an additional CFD cluster appears, representing the current trend in using software for modeling hydrodynamic systems.

Finally, in the third period, it becomes clear that the water quality cluster has positioned itself as a relevant theme. According to SDG 6, water quality is closely related to the population’s health and well-being, including drinking water and sanitation, hence the relevance of this cluster. In this period, the absorbent cluster also rises. This may be due to the requirement to remove pollutants that could not be identified before or that have recently appeared, an issue that is related to goal 6.3, where the objective is to improve water quality by reducing its pollution, and the adsorbent material development and application are efficient for this task.

Therefore, the evolution of water and waste water treatment scientific research associated with SDG 6 in Mexico and globally exposes shared priorities and distinct trajectories in research efforts and technological implementation. Basu and Dasgupta [43] reported that worldwide research has evolved from traditional water treatment and governance to include groundwater, waste water treatment, and integrated water resources management through emerging concepts like water security, the water-energy-food nexus, and ecosystem-based approaches.

Correspondingly, Mexican water and waste water treatment research in the Scopus publication timeline shows that at the early stages it was centered on basic water treatment, stabilization, and process control. Over time, Mexico has rapidly shifted the research priorities to advanced processes and contaminant-specific removal (e.g., nitrates, arsenic, azo dyes). Meanwhile, Belgian [18] and global research maintain a strong focus on SDG 6 targets connecting water with energy, food, and ecosystems. Finally, in Mexico, recent themes emphasize the importance of nanotechnology, advanced oxidation processes, microplastics, and circular economy, reflecting a shift towards innovative and sustainable solutions.

3.5. Impact on SDG 6 Targets and the Other Sustainable Development Goals

A classification was made of the published documents on the theme of water and waste water treatment concerning the particular targets of goal 6. This classification followed the methodology proposed by Ho et al. (2020), which could be used as a framework to optimize the analysis of scientific outputs in several regions concerning the 2030 Agenda [18].

Figure 8 shows the impact of the Goal 6 targets from the documents published in Mexican institutions. The figure also shows the contribution of water and waste water research in the three analyzed periods. Most documents contribute to targets 6.3 (water quality) and 6.5 (water resources management). A total of 1626 documents (first period: 125, second period: 402, and third period: 1099) contributed to target 6.3, and 1624 documents contributed to target 6.5 (124, 427, and 1073). The third most impacted target was 6.1, which relates to an essential intention: achieving access to drinking water.

On the contrary, it was found that the examined documents were less impactful to 6.b (participation of local communities), 6.2 (sanitation), and 6.a (international cooperation and capacity-building support to developing countries) targets. This might be because the selection of words in this bibliometric analysis (water and waste water treatment) could have filtered out research related to social issues such as community participation in procedures in regulations and policy, sanitation and defecation, and the existence of proper handwashing facilities, among others.

Regarding the significant topics that comprise the SDG 6, research conducted by Ho et al. in Belgium [18] reports that the publications were mainly related to targets 6.3, 6.4, 6.5, and 6.6, with the main hotspots for Belgian water research being water treatment, water stress, water pollution, climate change, and water modeling. Here, a remarkable difference with Mexico is observed, as the main impact is reflected on target 6.1, since universal and safe access to drinking water is still actively being researched. On the other hand, Basu and Dasgupta [43] coincide with this analysis as they report that targets 6.1, 6.3, and 6.5 are the most referred to. Our investigation found that Mexican publications also showed moderate contributions on targets 6.4 and 6.6.

Figure 9 shows the impact of documents related to water treatment research on the SDGs according to the queries proposed by Bedard-Vallee et al. mapping [28]. Of the 3813 documents, it was found that three SDGs were impacted the most by this research, and they are those related to Sustainable cities and communities (SDG 11), Industry, innovation and infrastructure (SDG 9), and Good health and well-being (SDG 3), with 668, 623, and 569 documents, respectively. The next group of impacted objectives is Responsible consumption and production (SDG 12), Affordable and clean energy (SDG 7), Life below water (SDG 14), and Life on land (SDG 15).

The impact towards these objectives is expected, especially the contribution of those related to sustainable communities, sustainable resource consumption, and the importance of water treatment for people’s health. Likewise, it is natural to associate these documents’ contributions with improving water and land life. On the other hand, it was observed that the impact on the climate change objective (SDG 13) appears in ninth place on the list; this is lower than initially expected. Finally, these works seem to have a marginal impact on achieving the objectives related to gender equality, reduced inequalities, and quality education. This can be associated with the technical wording in these published documents rather than with the fact that these investigations do not impact such pertinent issues.

Various strategies can be implemented to reduce net emissions, but the impacts and associated costs vary from region to region [44]. For example, the targets aimed at addressing people’s vulnerability, such as access to food, energy, water, and health services, or reducing poverty in all its dimensions, promise to be suitable for increasing resilience to climate change [45]. In addition, it is indicated that climate change is a risk multiplier since “It negatively impacts all SDGs and worsens most of humanity’s most pressing challenges such as poverty, hunger, drought, desertification, access to clean air, water energy, and more” [46].

Furthermore, scientific evidence identifies the benefits of addressing the SDGs and climate change actions synergistically, so that advances in any of these areas lead to improvements in the other and vice versa [47]. Also, it is necessary to evaluate the co-benefits and their possible climate compensations to increase the profitability of any intervention and support policy-makers and academics in developing viable strategies to address water and food security, urbanization, and energy generation and consumption.

Progress towards achieving the SDGs needed to catch up before the declaration of the COVID-19 pandemic. With COVID-19 [48], it became evident that some SDGs’ goals (food security, access to water, health services) are more pressing. In addition, during the recession during the pandemic, governments had to choose and prioritize between national needs and financing SDGs due to liquidity problems.

While Mexican research has strongly contributed to SDG 6 targets on water quality, resource management and access to drinking water, the analysis reveals significant gaps in other targets such as sanitation, community participation, and international cooperation. To better align future research with these under-addressed areas, it is recommended to (i) strengthen interdisciplinary studies that integrate technical innovations with social science approaches to sanitation and hygiene, (ii) expand research that involves and empowers local communities in water management projects, particularly in rural and marginalized regions, and (iii) foster international collaborative networks that translate bibliometric evidence into policy frameworks and technology transfer. By rebalancing research portfolios toward these targets, Mexican contributions can more comprehensively support SDG 6 and maximize synergies with other SDGs.

4. Conclusions

According to the bibliometric analysis, Mexican research related to water and waste water treatment initially focused on pathogen removal, emphasizing the efficiency, stability, and control of the treatment processes; therefore, some of the first achievements were made regarding access to drinking water and water quality. Subsequently, the interest shifted to pollutant removal processes such as arsenic and nitrates, water treatment, and reuse processes. Furthermore, in recent years,—and supported by technological development, researchers have focused on process optimization to guarantee the useful life of the water resource, evolving to cutting-edge topics such as advanced oxidation processes, nanotechnology, microplastics, bioeconomy, and circular economy, among others.

To sum up, a research trend observed throughout the Mexican research group’s history is related to technological development and the capacity to invest in its acquisition. Although technological advances have made it possible to identify several pollutants and various emerging compounds in effluents and water bodies throughout the country, there is a long way to go until these findings can be reflected in the current regulations.

All these research interests can be classified into the three main clusters that were identified; the first is related to general water treatment processes, especially physicochemical, the second is associated with biological issues of water treatment, and the third is focused on water sources, management, and use.

Moreover, it is noted that Mexican research contributes mainly to the achievement of the SDG 6 targets related to water quality (6.3), water resources management (6.5), and access to drinking water (6.1). Nevertheless, although research continues to advance, novel techniques and methodologies take time and are difficult to implement. For example, one of the most significant challenges in meeting the SDG 6 targets is the useful life span of the water distribution and waste water collection infrastructure. Despite new materials, tools, and technology for monitoring, operators still need proper public policies and more financial and human resources to implement them.

Meanwhile, at the international level, research is focusing on the water-energy-food nexus, water security, and the ecosystem water approach. Considering SGD 6 targets, it is evident that Mexico is still actively researching improving water quality and management, as well as achieving universal and safe access to drinking water, unlike other latitudes, where the research has evolved to themes related to water-use efficiency and water-related ecosystems, associated with 6.4 and 6.6 targets.

Research in Mexico, as in the rest of the world, will continue to advance towards proposing and implementing the improvement of water treatment systems. However, if the targets set out in SDG 6 are to be met, significant efforts should be made to develop accessible technologies. Attainable alternatives within all nations’ reach can increase their scope of application and affect a greater number of communities and populations, particularly rural areas and vulnerable citizens. Research efforts can move beyond the current emphasis on water quality and management to a more comprehensive engagement with all dimensions of SDG 6 by fostering interdisciplinary approaches, empowering local communities, and strengthening international collaborations. Such actions would ensure that scientific advances are effectively translated into tangible improvements in water governance, infrastructure, and equitable access, reinforcing Mexico’s capacity to achieve the SDG 6 targets by 2030.

Furthermore, Mexican research on water and waste water treatment has a positive impact on the achievement of global objectives, such as the improvement of communities (SDG 11), the improvement of infrastructure and innovation processes (SDG 9), and, very importantly, the impact on the general improvement of people’s health is observed (SDG 3). Finally, although Mexico is moving towards sustainable water development, and its impacts are noticeable, it is necessary to intensify community efforts and foster collaboration between society, the government (through public policies, regulations, and budgets), the private sector, and academia. By joining forces, it will be possible to substantially impact the integrated management of water resources, their quality, and sanitation to achieve the SDGs and, particularly, all of the SDG 6 targets by 2030.