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4.4 Variations or Patterns of Water Demand 133
About two-thirds of the total water intake of U.S. manufacturing plants is put to use
for cooling. In electric-power generation, the proportion is nearly 100%; in manufacturing
industries, it ranges from 10% in textile mills to 95% in beet sugar refineries. It averages
66% in industries as reported by the National Association of Manufacturers.
Industry often develops its own supply. Chemical plants, petroleum refineries, and
steel mills, for example, draw on public or private utilities for less than 10% of their needs.
Food processors, by contrast, purchase about half of their water from public supplies,
largely because the bacterial quality of drinking water makes it de facto acceptable.
About 90% of the industrial draft is taken from surface sources. Groundwaters may be
called into use in the summer because their temperature is then seasonally low. They may
be prized, too, for their clarity and their freedom from color, odor, and taste.
Available sources may be drawn on selectively: municipal water for drinking, sanitary
purposes, and delicate processes, for example; and river water for rugged processes and
cooling and for emergency uses such as fire protection. Treatment costs as well as eco-
nomic benefits are the determinants.

4.3.4 Rural Water Consumption

The minimum use of piped water in rural dwellings is about 20 gpcd (75 Lpcd); the aver-
age about 50 gpcd (190 Lpcd). Approximate drafts of rural schools, overnight camps, and
rural factories (exclusive of manufacturing uses) are 25 gpcd (95 Lpcd); of wayside restau-
rants, 10 gpcd (38 Lpcd) on a patronage basis; and of work or construction camps, 45 gpcd
(170 Lpcd). Resort hotels need about 100 gpcd (380 Lpcd), and rural hospitals and the like,
nearly twice this amount.
Farm animals have the following approximate requirements: dairy cows, 20 gpcd
(75 Lpcd); horses, mules, and steers, 12 gpcd (45 Lpcd); hogs, 4 gpcd (15 Lpcd); sheep,
2 gpcd (8 Lpcd); turkeys, 0.07 gpcd (0.26 Lpcd), and chickens, 0.04 gpcd (0.15 Lpcd).
Cleansing and cooling water add about 15 gpcd (57 Lpcd) for cows to the water budget
2
3
2
of dairies. Greenhouses may use as much as 70 gpd per 1,000 ft (2.856 10 3 m /d/m )
and garden crops about half this amount.
Military requirements vary from an absolute minimum of 0.5 gpcd (1.9 Lpcd) for
troops in combat through 2 to 5 gpcd (7.6 to 19 Lpcd) for soldiers on the march or in
bivouac, and 15 gpcd (57 Lpcd) for temporary camps, up to 50 gpcd (190 Lpcd) or more
for permanent military installations.

4.4 VARIATIONS OR PATTERNS OF WATER DEMAND
A pattern is a function relating water use to time of day. Patterns allow the user to apply au-
tomatic time-variable changes within the system. Most patterns are based on a multiplica-
tion factor versus time relationship, whereby a multiplication factor of 1.0 represents the
base value (often the average value, Q avg ). This relationship is written as Q kQ avg ,
t
where Q demand at time t and k multiplier for time.
t
Water consumption changes with the seasons, the days of the week, and the hours of
the day. Fluctuations are greater in small rather than large communities, and during short
rather than long periods of time. Variations are usually expressed as ratios to the average
demand. Estimates for the United States are as follows:

Ratio of Rates, k Normal Range Average
Maximum day: average day (1.5 to 3.5):1 2.0:1
Maximum hour: average day (2.0 to 7.0):1 4.5:1