PUB00013

• Year: 1985
• Title: Estimated Use of Water in Colorado 1985
• CWCB Section: Water Conservation & Drought Planning
• Author: David W. Litke and Cynthia L. Appel
• Description: Water-Resources Investigations Report 88-4101
• Publications - Doc Type: Brochure

water-withdrawal data. Missing information was estimated using a variety of
available supplemental information and by comparison with similar systems
elsewhere. Data also were estimated for the public-supply systems that were
not contacted directly. Population served, source of water, and average
system production for many of these systems were obtained from Colorado State
Department of Health records, although these data were not verified. Where no
production data were available, several per-person-per-day production esti-
mates (based on available data) were used: 200 gallons for small rural
systems using surface water; 150 gallons for small rural systems using ground
water; 125 gallons for large trailer courts; and 75 gallons for small trailer
courts. For small systems where no delivery breakdown was available, propor-
tions of 90 percent domestic,S percent commercial, and 5 percent other were
used.

12

Data about surface-water withdrawals by public-supply systems were
acquired from the State Engineer's Office. Water-production data (for
public-supply systems using surface water) compiled for this study were 15
percent less than withdrawal totals provided by the State Engineer's Office;
the additional withdrawn water probably is lost during conveyance to treatment
plants, is withdrawn but bypasses treatment plants, or is used in the plants
themselves. For example, five percent conveyance losses are charged by the
State Engineer's Office against water delivered by the Denver Water Department
in its southern collection system to account for seepage losses of raw water
(U.S. Army Corps of Engineers, 1986b, p. 32). Therefore, surface-water-
production data compiled as part of this study were increased by 15 percent so
that values agreed with withdrawals reported by the State Engineer's Office.
This additional water was included in the "other" water-use category. The
"other~ category also includes public-supply-system water for public use
(firefighting, municipal swimming pool uses, park irrigation, street
cleaning), and losses in the delivery systems. A survey of major Colorado
suppliers (American Water Works Association, 1981) found that delivery-
system losses of about 10 percent are common.

Of the 20,800 million gallons per day of water used during 1985, about
20,200 million gallons per day was self supplied and 737 million gallons per
day was public supplied. Of the self-supplied water, 62 percent was used for
irrigation, 36 percent for hydroelectric power generation, and the remaining 2
percent for other uses.

Public-supply system deliveries, by counties, are shown in figure 5. The
public-supply-system data also are summarized in table 3 (for counties) and
table 14 (for hydrologic subregions) in the "Supplemental Data" section at the
back of this report. Domestic and commercial deliveries amounted to 77
percent of water withdrawn by public-supply systems and are highly correlated
with population (correlation coefficient of 0.99 for domestic deliveries, 0.88
for commercial deliveries). That is, the counties with the largest deliveries
are those with the largest populations (Denver, Jefferson, Arapahoe, and El
Paso Counties). For the entire State, the average use rate for water with-
drawn by public-supply systems is 245 gallons per person per day. This value
is relatively large because it includes transmission losses of raw water and
distribution losses but still it compares fairly well with data reported by
previous studies. For example, use rates for northern Colorado towns along