Resilience in Water Infrastructures: A Review of Challenges and Adoption Strategies

: An increase in the number and strength of natural catastrophes experienced over the past few decades has accelerated the damage sustained by infrastructures. Drinking water and wastewater infrastructure systems are critical aspects of a healthy environment, and their ability to withstand disasters is vital for effective disaster response and recovery. Although numerous studies have been conducted to determine the challenges that natural disasters render to water infrastructures, few extensive examinations of these challenges have been conducted. The goal of this study, therefore, was to identify and categorize the challenges related to the resilience of drinking water and wastewater infrastructures, and to determine the strategies that most effectively minimize their unintended consequences. A comprehensive evaluation of the existing literature was conducted, and 537 publications were collected. After extensive screening, 222 publications were selected for rigorous evaluation and analysis based on the data collection methods and other criteria. A total of ﬁfty-one (51) challenges were determined and classiﬁed, within the following ﬁve categories: environmental, technical and infrastructure, social, organizational, and ﬁnancial and economic. The challenges were then ranked within each category according to their frequency of occurrence in previous research. The results reveal that climate change, aging infrastructure, lack of infrastructure capital, population growth, improper maintenance of water infrastructure, and rapid urbanization are the most frequently cited challenges. Next, 30 strategies and approaches were identiﬁed and categorized into either preventive or corrective actions, according to their implementation time. The ﬁndings of this study will help decision-and policymakers properly allocate their limited funding to enhance the robustness of their water infrastructures before, during, and after natural hazards.


Introduction
The U.S. government enacted the Clean Water Act in 1972 and the Safe Drinking Water Act in 1974 to provide its citizens with safe and clean water [1]. Since then, attempts have been made to protect the water infrastructure and provide safe water for the healthy functioning of society. Safe, clean water is an essential part of our day-to-day lives. Reinforcing and preparing the water infrastructure for any sort of circumstance and making our drinking and wastewater infrastructure resilient in the face of natural hazards is of great importance [2,3]. It is crucial to health, as it secures the environment, increases economic growth by providing employment opportunities, and provides individuals with water that can be used for a variety of purposes (drinking, cooking, and recreation) [4,5].
Natural hazards are occurring more frequently, and we cannot keep them from occurring [3,6], which results in a transition in risk management. Rather than decreasing exposure or the odds of a hazard occurrence, decision-makers are increasingly focusing on strengthening the resilience and reducing the vulnerability of infrastructures [7]. Over time, various definitions of and approaches to resilience have been touted. From the point of view of [8], the capacity to minimize the size and intensity of natural disasters is referred to Figure 1 depicts the systematic research framework that was developed to fulfill this study's objectives. A thorough literature search was conducted, using search engines, including Google Scholar, Science Direct, Scopus, Inspec, and ProQuest, to acquire relevant articles. The selected publications were then scrutinized based on the journal's name, data collection method, and year of study. After the five main objectives were achieved and studied, the results were analyzed and discussed.

Research Methodology
Sustainability 2021, 13, x FOR PEER REVIEW 2 of 16 of view of [8], the capacity to minimize the size and intensity of natural disasters is referred to as infrastructure resilience. The ability of a resilient infrastructure or organization to foresee, endure, adjust to, and swiftly recover from a potentially disastrous incident determines its efficacy.
In the opinion of researchers [9], the progress of human society is associated with critical infrastructure. Researcher [10] took this one step further by espousing that the maintenance of critical infrastructures is vital for the socio-economic system. According to the United States Environment Protection Agency (USEPA), the United States has spent billions of dollars to replace, repair, and maintain drinking water, wastewater, and the stormwater infrastructure during the past few years. The requirement for an infrastructure investment is justified, as water is crucial to Americans' physical and economic lives [11]. Most existing distribution lines, treatment plants, and sewer lines are at least 100 years old. The replacement era has arrived, and our common concern now is to meet public health and other programmatic goals [12]. At present, all government levels are taking steps toward building resilient infrastructures and communities [13].
The following objectives were developed to determine the challenges and strategies that contribute to the resilience of drinking water and wastewater infrastructures: (1) identify the challenges, (2) classify the challenges, (3) prioritize and rank the challenges based on the frequency with which they appear in the literature, (4) identify the strategies and approaches, and (5) classify the strategies and approaches based on the time of their implementation. This study can significantly help researchers and management authorities to be aware of the challenges and management strategies that can enhance the resilience of the drinking water and wastewater infrastructure. Figure 1 depicts the systematic research framework that was developed to fulfill this study's objectives. A thorough literature search was conducted, using search engines, including Google Scholar, Science Direct, Scopus, Inspec, and ProQuest, to acquire relevant articles. The selected publications were then scrutinized based on the journal's name, data collection method, and year of study. After the five main objectives were achieved and studied, the results were analyzed and discussed.

Data Collection
The selection and review process of articles for this research are depicted in Figure 2. It began by entering the following keywords into multiple search engines to gather pertinent scholarly articles: resilience of water infrastructure, drinking water, wastewater, challenges to the resilience of drinking water and wastewater infrastructures, and strategies to enhance the water infrastructure resilience. As a result, 537 published journal articles, conference proceedings, dissertations, and research reports on the resilience enhancement of drinking water and wastewater infrastructures were collected. First, the authors excluded the works published before the year 2000, as most of the challenges and strategies discussed in the published articles after the year 2000 covered those discussed in studies published before the year 2000. Next, the titles and abstracts were reviewed by the authors, and relevant articles were included. Lastly, the authors screened full-text papers, and 222 articles were retained for a detailed review.

Data Collection
The selection and review process of articles for this research are depicted in Figure 2. It began by entering the following keywords into multiple search engines to gather pertinent scholarly articles: resilience of water infrastructure, drinking water, wastewater, challenges to the resilience of drinking water and wastewater infrastructures, and strategies to enhance the water infrastructure resilience. As a result, 537 published journal articles, conference proceedings, dissertations, and research reports on the resilience enhancement of drinking water and wastewater infrastructures were collected. First, the authors excluded the works published before the year 2000, as most of the challenges and strategies discussed in the published articles after the year 2000 covered those discussed in studies published before the year 2000. Next, the titles and abstracts were reviewed by the authors, and relevant articles were included. Lastly, the authors screened full-text papers, and 222 articles were retained for a detailed review.  Table 1 shows a distribution of the articles according to their sources and scientific field and shows that the authors enhanced the study database by analyzing various articles. The top five selected journals were Water, Journal of Infrastructure Systems, Journal of Water Resources Planning and Management, Water Research, and Water Science and Technology, representing 11%, 10%, 10%, 8%, and 7% of the articles in the database, respectively. The publishers of the peer-reviewed journals are the Multidisciplinary Digital Publishing Institute (MDPI), the American Society of Civil Engineers (ASCE), Elsevier, and the International Water Association.  Table 1 shows a distribution of the articles according to their sources and scientific field and shows that the authors enhanced the study database by analyzing various articles. The top five selected journals were Water, Journal of Infrastructure Systems, Journal of Water Resources Planning and Management, Water Research, and Water Science and Technology, representing 11%, 10%, 10%, 8%, and 7% of the articles in the database, respectively. The publishers of the peer-reviewed journals are the Multidisciplinary Digital Publishing Institute (MDPI), the American Society of Civil Engineers (ASCE), Elsevier, and the International Water Association.

Data Collection Method
The most often used approaches for data collection are literature reviews, surveys, interviews, questionnaires, experiments, observations, and case studies. Figure 3 illustrates the distribution of published articles based on their data gathering procedures. Literature review is the most common method of data collecting, accounting for 36% of all publications. Surveys and interviews are the second most frequently used practice, contributing to 32% of all practices. Case studies rank third, comprising 18% of all practices, while only 14% of data is gathered through experiment and observation.

Year of Study
As presented in Figure 4, articles published from 2000-2020 were analyzed and sorted into two-year intervals. From Figure 4, it is evident that there was a constant increase in the number of publications after 2010; however, the highest frequency of publications (45) occurred between 2019 and 2020. As the need for a more resilient water infrastructure grows in tandem with the growing number of global difficulties, efforts are being made to understand the causes of the increased frequency of disasters and develop approaches to overcome them.

Year of Study
As presented in Figure 4, articles published from 2000-2020 were analyzed and sorted into two-year intervals. From Figure 4, it is evident that there was a constant increase in the number of publications after 2010; however, the highest frequency of publications (45) occurred between 2019 and 2020. As the need for a more resilient water infrastructure grows in tandem with the growing number of global difficulties, efforts are being made to understand the causes of the increased frequency of disasters and develop approaches to overcome them.
As presented in Figure 4, articles published from 2000-2020 were analyzed and sorted into two-year intervals. From Figure 4, it is evident that there was a constant increase in the number of publications after 2010; however, the highest frequency of publications (45) occurred between 2019 and 2020. As the need for a more resilient water infrastructure grows in tandem with the growing number of global difficulties, efforts are being made to understand the causes of the increased frequency of disasters and develop approaches to overcome them.

Identification and Classification of Challenges to Drinking Water and Wastewater Infrastructure Resilience
The full texts of the gathered papers were evaluated to determine the challenges to the resilience of the drinking water and wastewater infrastructure. A total of fifty-one (51) challenges were determined and categorized into five groups: environmental, technical and infrastructure, social, organizational, and financial and economic. The challenges were then ranked within each category according to their frequency of occurrence in previous research. For example, rank one indicates the most commonly stated challenge in

Identification and Classification of Challenges to Drinking Water and Wastewater Infrastructure Resilience
The full texts of the gathered papers were evaluated to determine the challenges to the resilience of the drinking water and wastewater infrastructure. A total of fifty-one (51) challenges were determined and categorized into five groups: environmental, technical and infrastructure, social, organizational, and financial and economic. The challenges were then ranked within each category according to their frequency of occurrence in previous research. For example, rank one indicates the most commonly stated challenge in the reviewed literature. Tables 2-6 summarize the categories, challenges, frequencies, and rankings.

Environmental
Ecosystems and the environment contribute significantly to the wellbeing of humankind [14]. For example, risk reduction and resilience in the face of disasters can be accomplished through an effective ecosystem and environmental management. However, as presented in Table 2, the environmental category consists of ten challenges, among which climate change (E1) was noted 55 times as a significant challenge in the reviewed literature. Changes in the environment create new obstacles and lengthen the recovery time of the reconstruction process, and as we are not usually able to foresee natural catastrophes or their severity, it is vital to be prepared for any type of disaster. Any alterations in the climate impact society, the economy, and the environment, and our changing climate is one of the critical challenges to achieving and maintaining a resilient water infrastructure [29]. Flooding and vulnerability to heavy rains was the second most cited challenge of the environmental category. A resilient infrastructure should be able to withstand and recover from any kind of future disaster, but the history of damages created by floods shows us how weakly our engineering and economic systems were designed (Jonkman and Dawson 2012). The need for infrastructures that are resilient to floods is greater than ever because of the increasing number of floods and the intensity of damages that they wreak. To fully comprehend and quantify flood risks, flood maps, along with a comprehensive analysis of loads and inundations, and an impact analysis, is needed [16].
Extreme weather conditions are the third most noted barrier of this category. They consist of either the highest or the lowest temperatures that will cause a surge in extreme weather events, such as floods, droughts, wildfires, erosion, turbidity, collection of debris, and many more issues [18]. These conditions are hard to manage and negatively impact water quality, thereby endangering human health [19]. The next most frequently referred to environmental challenges are droughts and earthquakes, respectively. The authors of [20] noted that earthquakes and droughts have the most risk factors for water infrastructures, as any disaster that causes damage to significant aqueduct systems will have a greater impact on the supply of water.

Technical and Infrastructure
The infrastructure refers to a collection of systems and networks, such as water distribution, energy production, telecommunications, and transportation, which are vital to the function of society. Inadequate operation of various infrastructures can have a detrimental effect on all of an area's activity. Although the recovery process after a disaster facilitates the establishment of robust infrastructures, it is frequently fraught with barriers [30]. As shown in Table 3, the technical and infrastructure category includes twelve challenges. The most frequently cited challenge is an aging infrastructure. The issue of an aging infrastructure has grown more significant in recent years. Many infrastructures and equipment were developed or installed in the 1950s and early 1960s [31], and are reaching the end of their usefulness. However, developing a sustainable infrastructure demands a considerable financial investment to keep the essential infrastructure components and networks in excellent working order [32] The next most frequently cited barrier of this category is improper maintenance of the water infrastructure. The direct proportion between the aging infrastructure and its maintenance is creating large barriers. The authors of [4] cited that a poor maintenance program might pose an external danger to water users and regulators; therefore, proper infrastructure management and maintenance must be considered as one of the significant challenges to the drinking and wastewater infrastructure [33]. The use of traditional wastewater treatment technologies is the third most often cited challenge [34]. Conventional methods such as water-flush toilets, combined sewerage, and centralized treatment have not been harmonized, and diluting pathogen-and hazardous-substance-containing wastewater streams, such as heavy metals and organic micropollutants, complicate treatment [35].
The interdisciplinary nature of a critical infrastructure is the fourth most mentioned barrier of this category, and it needs a greater understanding as it creates real challenges around the domain [37]. To begin with, there is no unified lexicon, thus multiple names for the same notion might exist. Similar terms can have distinct meanings, which necessitates constant translation, and as a result, attempting to integrate findings that are based on mutually compatible assumptions is sometimes challenging [36].
Escalating physical threats to the water infrastructure is the next most commonly discussed technical and infrastructure barrier. As physical risks are increasing, it is essential to create strategies that can detect the multifaced cyber and physical threats that cause damages to physical components, such as pumps, valves, tanks, as well as to the supply and quality of water [39].

Social
The social science literature defines resilience as "the intricate network of social connections, characteristics, and capacities that enable a community to adapt to the hazards it faces" [47,48]. As a result, communities must be prepared for disaster mitigation and resilience building in order to avoid the most adverse impacts of disasters and recover as quickly as possible. As shown in Table 4, population growth was discussed 47 times in the reviewed literature as one of the most critical challenges. In the studies conducted by [4,49,50], population growth was mentioned as the greatest challenge to the water infrastructure because it has made ensuring water quantity and quality increasingly difficult. Rapid urbanization was the second most cited social issue because it results in rapid population growth [51]. Effective urban water policies and designs that can be adapted to changes in needs are essential to managing the water infrastructure issues caused by an increase in population and urbanization [52]. For example, due to urbanization, climate change results in increased rainfall and an increase in impermeable surfaces, both of which contribute to a decrease in the resilience of a system [60].
The public's lack of awareness and knowledge about disaster response and recovery adds to the recovery time and was identified as third most cited social barrier. Having a mentally strong society builds encouragement and trust among its members. The authors of [12,53] believe that implementation of the resilience concept, and maintenance and promotion of sustainable infrastructures are imperative actions that should be put forward in designing drinking water infrastructures.
Lack of community engagement and responsibility and a drastic increase in the demand for water are the next most often cited social challenges. A lack of community engagement results in a respective decline in the quality and quantity of services and re- sources received in response to the disaster [55,61]. Furthermore, as the demand for water increases, it places a burden on the maintenance and distribution of water for domestic, agricultural, industrial, and recreational purposes, posing a threat to the existing infrastructure and challenging the design and construction of future infrastructural facilities [62,63].

Organizational
The organizational category encompasses thirteen challenges, among which the most frequently cited was lack of data reliability, quality, and accessibility, as shown in Table 5. According to [64], obtaining meaningful and reliable data has always been a problem in quantifying resilience. In the same way that data from risk and vulnerability analyses assists decision-makers in recognizing problems, vulnerabilities, and allocating resources, the lack of quality information has a detrimental effect on society and other interdependencies [7,65].
Pooling risks in a professional service provider is the second most cited organizational barrier. The author of [66] says that pluralist institutions attempt to create fulfilling solutions to rural water issues for diverse ways of organizing, particularly as it relates to operational and financial concerns, through risk pooling and networking at scale. Currently, the performance of a water and wastewater utility is determined not only by the delivery of basic services or the processing of wastewater with sufficient quality levels, but also by other factors such as sustainability [35]. Thus, a lack of sustainability and system planning is the third most mentioned barrier in this category, as failures in the planning process can cause negative consequences [68].
As presented in Table 5, the speed and scale of a response is the next most cited organizational barrier, and [69] espoused that the construction industry faces these challenges. The reasons behind the delays in response time are an inappropriate water infrastructure, disparities in the performance and unmonitored self-supply, lack of sustainable and innovative system planning, and pooling risks in a professional service provider [57].
Poor solid waste management is the fifth most referred to barrier in the organizational category. Solid waste management is a problem for metropolitan regions of all sizes, from megacities to tiny towns and big villages [46]. Cities produce enormous volumes of solid garbage and have everything from non-existent collection methods to inefficient disposal that pollutes the air, water, and land. Open and filthy landfills lead to the pollution of drinking water, as well as to the spread of illness and sickness [51].

Financial and Economic
The financial and economic category includes six challenges that might be considered as economic indicators for a successful recovery. As illustrated in Table 6, the lack of infrastructure capital was the most-cited financial and economic barrier, with the frequency Sustainability 2021, 13, 12986 9 of 15 of 49. Adequate funding is absolutely vital to the extensive investments that will be necessary to repair old infrastructures, bring them into compliance with more stringent health and environmental laws, and ensure future service quality [36]. As presented in Table 6, the next two most cited challenges are related to the population's low economic status and unemployment issues [70]. The author of [75] cited that human health is at risk due to inappropriate access to portable water, particularly in low-and middle-income nations as economic issues such as unemployment hinder the procurement of safe drinking water [70]. The inability to pay utility bills, socio-economic status, and competition for local employment are the last three significant challenges of this category. A state's capacity to respond to the rising water-sector demands is hampered by non-existent financial resources [76]. When utility customers do not pay their bills, it is difficult (or impossible) for municipalities to continue delivering services [70]. Furthermore, the interlinking nature of the socio-economic status is responsible for the unequal distribution of infrastructure facilities in many developing countries. This discrepancy in the socioeconomic status makes it harder for people in low-income groups to manage emergency resources during recovery from a disaster [78].

Top Five Highest Frequency Challenges
The top five most frequently cited challenges, depicted in Figure 5, fall into five categories: environmental, technical and infrastructure, financial and economic, social, and organizational. Climate change (E1), which belongs to the environmental category, scored the highest frequency (55); aging infrastructure (T1), which falls under the technical and infrastructure category, received the second-highest frequency (51); and lack of infrastructure capital (FE1), which belongs to the financial and economic category, received the third-highest frequency (49) among all identified challenges.  As presented in Table 6, the next two most cited challenges are related to the population's low economic status and unemployment issues [70]. The author of [75] cited that human health is at risk due to inappropriate access to portable water, particularly in lowand middle-income nations as economic issues such as unemployment hinder the procurement of safe drinking water [70]. The inability to pay utility bills, socio-economic status, and competition for local employment are the last three significant challenges of this category. A state's capacity to respond to the rising water-sector demands is hampered by non-existent financial resources [76]. When utility customers do not pay their bills, it is difficult (or impossible) for municipalities to continue delivering services [70]. Furthermore, the interlinking nature of the socio-economic status is responsible for the unequal distribution of infrastructure facilities in many developing countries. This discrepancy in the socioeconomic status makes it harder for people in low-income groups to manage emergency resources during recovery from a disaster [78].

Top Five Highest Frequency Challenges
The top five most frequently cited challenges, depicted in Figure 5, fall into five categories: environmental, technical and infrastructure, financial and economic, social, and organizational. Climate change (E1), which belongs to the environmental category, scored the highest frequency (55); aging infrastructure (T1), which falls under the technical and infrastructure category, received the second-highest frequency (51); and lack of infrastructure capital (FE1), which belongs to the financial and economic category, received the third-highest frequency (49) among all identified challenges.

Strategies and Approaches for Achieving a Resilient Drinking Water and Wastewater Infrastructure: Preventive and Corrective Actions
Appropriate strategies and approaches, based on the identified challenges, can be implemented to enhance the resilience of the drinking water and wastewater infrastructure. Preventive strategies should be adopted prior to a disaster, while corrective methods should be implemented following a disaster. Of the 30 strategies and approaches that were found to be effective, seventeen (17) were classified as preventive, while the other thirteen (13) were classified as corrective, based on their implementation time. Table 7 presents the strategies and approaches in terms of their application, time of implementation, and the related challenges. Accurate sustainable system planning Corrective O3 [68] As presented in Table 7, a Geographic Information System (GIS) prevents the challenges of aging infrastructure (T1), the interdisciplinary nature of infrastructure (T4), and physical threats (T6) by transforming and integrating geographical data and value judgments [79]. GIS may be used to categorize the shape, age, and condition of sewage and the wastewater infrastructure and give managers and engineers a graphical representation of the attributes. It can also be used to support a wastewater system and local conditions, as well as define the most vulnerable manholes and pipes in a county's wastewater system [57]. It is predicted that GIS solutions for wastewater and sewage utilities will become the norm in the next decade. Table 7 depicts that examining decisions on management techniques is a corrective action that addresses the challenges of climate change (E1), droughts (E4), earthquakes (E5), and direct and indirect lack of water (E9). As we cannot usually foresee natural catastrophes and their severity, it is vital to be prepared for any type of disaster, and the construction of sustainable and resilient wastewater structures is critical [15]. To assess resilience, decisions on management techniques and technology for water and sanitation services must be examined for their sensitivity and adaptive capabilities [29].
Mary Douglas's Culture Theory is another preventive approach that is shown in Table 7. It can be used to manage rural water points and to investigate how it may be operationalized in pluralist arrangements in scaling up different management cultures [84]. It describes how various management cultures deal with organizational, financial, structural, and environmental hazards [85], and illustrates the possibility for risk-sharing in a professional service provider and decreasing uncertainty by enabling quick reactions to waterpoint failures via newly discovered knowledge flows [66]. Table 7 shows that educating people about disaster responses and recovery strategies can help prevent a community's lack of trust, negative public opinion, and an inadequate number of qualified human resources. As the lack of public awareness and knowledge about hazards was one of the potential challenges, the implementation of measures to educate people about disaster response and recovery is vital, as being knowledgeable about available resources and how to access them will enable them to cope with the fallout from disasters [80,81]. Table 7 also indicates that SYNOPYSIS could be a corrective approach for addressing the challenges of shortages of supporting tools and systems (O11) and lack of an integrated framework and technological solutions (O12). It is a software package for synchronous optimization and simulation of urban wastewater systems that contains sewage system, treatment plant, and river sub-models that are largely based on modelling techniques [4]. It also shows how typical standards software might produce erroneous results when assessing the functioning of urban wastewater systems under varied conditions [2].

Conclusions
This study sought to determine the challenges to a resilient drinking water and wastewater infrastructure. The database identified 51 challenges and classified them into five categories: environmental, technical and infrastructure, organizational, social, and financial and economic. A total of thirty (30) strategies and approaches that effectively address the challenges were determined and categorized into preventive and corrective groups, based on implementation time.
The results revealed that climate change was the most referred to barrier in the environmental category, as changes in the climate create new obstacles and lengthen the reconstruction process. An aging infrastructure was the most frequently mentioned barrier in the technical and infrastructure category. Many structures are reaching the end of their lifetime, and a considerable financial investment will be needed to keep them back in excellent condition. The most significant barrier of the social category was population growth. Due to the increase in the population, it is increasingly difficult to ensure the quality and quantity of water. The top-ranked barrier in the organization category was the lack of data reliability, quality, and accessibility. Lack of reliable data has always been a problem in quantifying resilience and negatively impacts society. Finally, the lack of infrastructure capital was the top-ranked barrier in the financial and economic category. Insufficient capital causes major challenges by delaying resources such as materials, machinery, and workforce. Among the 30 identified strategies and approaches, 17 are preventive and 13 are corrective. The findings of this paper will assist engineering research communities in developing more accurate, quantitative, and practical resilience measures for critical water infrastructures. While great care was taken to conduct a thorough and reliable study, there are a few limitations that should be mentioned. The challenges of the financial and economic category were not studied in detail by the researchers, but because of their significance, it is recommended that additional attention be paid to them in future studies.
Additionally, the dynamic relationships between the various challenges and strategies must be investigated.
Author Contributions: Conceptualization, A.P., E.S. and N.A.; methodology, A.P.; writing-original draft preparation, A.P., N.A., and E.S.; writing-review and editing, S.K.; supervision, S.K. All authors have read and agreed to the published version of the manuscript.