A Benchmarking System for Domestic Water Use
- <80 L/person/day for Levels 5 and 6 (the best performing benchmarks);
- <105 L/person/day for Levels 3 and 4 (mid-range benchmark);
- <125 L/person/day for Levels 1 and 2 (lowest performing benchmarks).
- 8 min in a highly water efficient shower;
- 4 min in a standard shower;
- 2 min in a power shower;
- 30 min in a quarter filled 230 L bath.
- Step 1: Define a benchmarking system (using a band rating approach) for domestic mains water use performance of an individual (Section 2.1);
- Step 2: Five design cases (high to low water use) are developed for an “individuals” domestic demand (Section 2.2):
- The role of “Technological efficiency” and “User behaviour” is identified;
- The respective performance of an individual is plotted within the proposed band rating system and used as the baseline against which the sensitivity analysis (Step 3) is performed.
- Step 3: Sensitivity analysis (Results in Section 3):
- By using the five design cases, the influence on mains water demand and water band rating from using mains, Grey water (GW) and Rainwater harvesting RWH (in isolation and combination) is assessed;
- This includes investigating the influence of changes to:
- Rainfall in 3 Geographical locations (Midlands, South East, North West);
- Roof size (12.5 to 100 m2);
- Occupancy rates (1 to 4);
- Garden size (25 to 100 m2).
- Step 4: Discussion in light of results (Section 4).The following additional assumptions are made for the domestic property (unless stated otherwise):
- Internal demands only are included;
- 2.4 occupants per household ;
- Potable demands are met through mains water alone;
- Non-potable demands (including gardening) can be met in four different ways as listed below:
- Option 1—Mains only supply, for all non-potable needs (i.e., no RWH and/or no GW);
- Option 2—GW for WC flushing, first rinse on washing machine and gardening;
- Option 3—RWH for WC flushing, washing machine and gardening;
- Option 4—GW for WC flushing & RWH for washing machine and gardening.
- A pitched roof for rainwater collection with a 90% runoff coefficient ;
- Tank(s) are sized according to British Standard BS 8515, 2009 —this uses the lesser of 5% annual rainfall and non-potable demands. It is assumed that an empty tank is installed in January, it has been in operation for at least 12 months, and is filled/emptied assuming a “yield before spillage” approach [19,20,21];
- Rainfall and Temperature data are taken directly from the UK met-office  and use average monthly values of rainfall over 25 years (up to 2012) to calculate a daily average supply of rainwater. (n.b. stored water dictates available supply whilst spare capacity dictates flash flood protection, the influences of which can are reported by Hunt et al. [23,24] Consideration of the RWH supplies in July is adopted—this being the driest average month within the UK;
- Garden watering demand is based upon a generic model developed by Food and Agriculture Organization (FAO)  by which monthly climatic data are translated into a soil water balance for a given month [26,27]. The availability of water for any given plant type (assumed here to be grassland, flowers and shrubs) is a function of available soil water (root zone for grass is relatively shallow, i.e., <50 mm), rainfall and evapo-transpiration (ET) for each plant type (calculated according to Blaney Criddle method, see Doorenbos and Pruit . ET is influenced by temperature which is, as rainfall, location specific.
2.1. Step 1: Define a Benchmarking System (Using a Band Rating Approach)
2.2. Step 2: Development of Five Design Cases for Domestic Demand
|End Use||Units (L—Litres)||Design Case|
|WC a,b||L/flush||6 (0)||6 (0)||4.5 (−25)||2.6 (−57)||2.6 (−57)|
|Shower a,b||L/minute||24 (+100)||12 (0)||8 (−33)||6 (−50)||6 (−50)|
|Bath a,b||L||230 (0)||230 (0)||116(−50)||97 (−58)||None (−100)|
|Dishwasher b||L/setting||1 (0)||1 (0)||0.67 (−33)||0.67 (−33)||None (−100)|
|L/kg||13 (0)||13 (0)||10 (−23)||6.1 (−53)||6.1 (−53)|
|Sink a *||L/day||10.4 (0)||10.4 (0)||10.4 (0)||10.4 (0)||10.4 (0)|
|Basin a *||L/day||1.7 (0)||1.7 (0)||1.7 (0)||1.7 (0)||1.7 (0)|
|S1u||S2 u||S3 u||S4 u||S5 u|
|WC||Flushes/p/day||4.42 (0)||4.42 (0)||3.31 (−25)||1.90 (−57)||1.90 (−57)|
|Shower||Minutes/p/day||8.74 a (+100)||4.37 b (0)||2.93 c(−33||2.19 d(−50)||2.5 (−50)|
|Bath||Capacity/p/day||0.11e (0)||0.11 (0)||0.06 (−50)||0.05 (−58)||None (−100)|
|Dishwasher||Use/ps/p/day f||3.6 (0)||3.6 (0)||2.4 (33)||2.4 (33)||None (100)|
|Washing machine||Use/p/day f||2.1(0)||2.1 (0)||1.6 (−23)||0.99 (−53)||0.99 (−53)|
2.2.1. User Technologies
2.2.2. User Behaviour
3.1. Influence of Supply
3.2. Influence of Roof Size
3.3. Influence of Geographical Location: Rainfall
3.4. Influence of Occupancy Rates
3.5. Inclusion of External (Gardening) Demands
3.5.1. Influence of Time of Year
3.5.2. Influence of Garden Size (and Location)
3.5.3. Influence of Occupancy (and Location)
4.1. Technology and User Behaviour
- What is the lower limit to a showers flow rate, has it been reached?
- Can a very low flow rate shower (i.e., < 6 L/min) deliver the same shower experience as a 12 L/min or even a 24 L/min power shower? If not, then would acceptability and widespread adoption be inhibited?
- Is a (re)design (e.g., aeration technology) possible to deliver the same user-experience and function (i.e., personal washing and relaxation)?
4.4. Feasibility and Acceptability of a Benchmarking Approach (Using Band Ratings)
Conflicts of Interest
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Hunt, D.V.L.; Rogers, C.D.F. A Benchmarking System for Domestic Water Use. Sustainability 2014, 6, 2993-3018. https://doi.org/10.3390/su6052993
Hunt DVL, Rogers CDF. A Benchmarking System for Domestic Water Use. Sustainability. 2014; 6(5):2993-3018. https://doi.org/10.3390/su6052993Chicago/Turabian Style
Hunt, Dexter V. L., and Christopher D. F. Rogers. 2014. "A Benchmarking System for Domestic Water Use" Sustainability 6, no. 5: 2993-3018. https://doi.org/10.3390/su6052993