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128 Chapter 4 Quantities of Water and Wastewater Flows
8. Water quality for domestic and industrial purposes
9. Distribution-system pressure
10. Completeness of metering
11. Systems management.

4.3.1 Domestic Consumption

Although domestic water use is about 50% of the water drawn in urban areas, 90% of the con-
sumers are domestic. A breakdown of household flows apportions the various uses as follows:
1. 41% to flushing toilets
2. 37% to washing and bathing
3. 6% to kitchen use
4. 5% to drinking water
5. 4% to washing clothes
6. 3% to general household cleaning
7. 3% to watering lawns and gardens
8. 1% to washing family cars
Although domestic use is commonly expressed in gpcd (or Lpcd), the daily draft per
dwelling unit, gpud (or Lpud), may offer more meaningful information.
Extremes of heat and cold increase water consumption: hot and arid climates by fre-
quent bathing, air conditioning, and heavy sprinkling; and cold climates by bleeding water
through faucets to keep service pipes and internal water piping from freezing during cold
spells. In metered and sewered residential areas, the observed average daily use of water
for lawns and gardens, Q sprink1ing , in gpd during the growing season is about 60% of the es-
timated average potential evapotranspiration E, reduced by the average daily precipitation,
P, effective in satisfying evapotranspiration during the period, or
4
Q sprinkling 1.63 l0 A(E P) (U.S. Customary Units) (4.18)
where
Q sprinkling average daily use of water for lawns and gardens (gpd)
4
1.63 l0 number of gallons in an acre-inch considering a 60% factor
A average lawn and garden acreage per dwelling unit
E average potential evapotranspiration expressed (in./d)
P average daily precipitation (in./d)
The following is a sister equation using SI units:
Q sprinkling 6003 A(E P) (SI Units) (4.18a)
where
Q sprinkling average daily use of water for lawns and gardens (L/d)
A average lawn and garden area per dwelling unit (ha)
E average potential evapotranspiration expressed (mm/d)
P average daily precipitation also expressed (mm/d).
The average lawn and garden area per dwelling unit A is given by the observational
relationship
A 0.803D 1.26 (U.S. Customary Units) (4.19)