An Economic Development Strategy for the Sustainable Use of Water in the Paso del Norte Region
Residential Water Use & Assessment
Prepared by: Anthony J. Tarquin, Ph.D.
Professor of Civil Engineering
University of Texas at El Paso
March 1997
The following report was prepared as part of a project called "An Economic Development Strategy for the Sustainable Use of Water in the Paso del Norte Region," funding for which was provided, in part, by the U. S. Department of Commerce's Economic Development Administration (EDA). The statements, findings, conclusions, recommendations, and other data in this report are solely those of the authors, and do not necessarily reflect the views of the Economic Development Administration.

Introduction:

        There are many factors which affect the use of water but arguably the most important is population. For a specified renewable water amount, the population that could sustainably be served is dependent upon the average per capita water use rate which in turn, is dependent upon a number of other factors. In this report, some of those factors are considered and included along with other information for decision-making relative to sustainable populations in the Southern New Mexico, West Texas, Northern Mexico region.

Water Requirements:

        The first step in determining a regional sustainable population is assessing the available renewable water supplies. In this region, the renewable water comes from two sources: the Rio Grande and recharge into the Hueco and Mesilla bolsons. These amounts of water have been extensively studied (and continue to be so), but for purposes of the report, values of 600,000 and 25,000 acre-feet per year, respectively, will be used.

        Next, the amount of water used per person must be established. Table 1 shows two different scenarios for various water use categories identified as "realistic" and "optimistic."

Table One:  Water Requirements
 
Water Use Category
Amount
in gpcd
Realistic
Optimistic
I.
RESIDENTIAL
Toilets (1)
8
8
Toilet Leakage (10)
0.5
0
Shower (2)
12
3
Other Personal Cleanliness (3, 4, 5)
9.3
8
Cooking (10)
2
2
Drinking (10)
1
1
Dishwashing (6)
3
2
Laundry (7)
13
10
Cooling (8)
10
5
Landscape Irrigation (9)
54
5
Car Washing (10)
1
1
Miscellaneous (cleaning floors, watering houseplants, etc.)
2
2
TOTAL RESIDENTIAL
116
47
II.
COMMERCIAL @ 16%
28
?
III.
INDUSTRIAL @ 11%
19
?
IV.
GOVERNMENTAL USE @ 7%
12
?
V.
LOSSES @ 7%
12
12
T O T A L
187
59 +
Assumptions:         The realistic scenario for residential use is, as the name implies, achievable with relatively little change in the prevailing quality of life issues. The optimistic scenario on the other hand, would entail a considerable alteration in existing behavior patterns. The assumptions underlying the numbers are listed for all of the water use categories at the end of the table.

        As shown in the table, the water use amounts for the realistic and optimistic scenarios are 187 and 59+ gallons per capita per day (gpcd), respectively, depending upon what is assumed for the commercial, industrial, government, and loss categories. In order to relate these numbers to a sustainable population, a graph of population versus average water use per person was plotted for three different water supply amounts as shown in Figure 1. The three water amounts used were as follows:

        For scenario number 3, the 55% figure for agricultural use was arrived at by considering a conversion rate of 3,000 acres of agricultural water rights lands per year for 30 years to Municipal and Industiral (M&I) use (El Paso's historic acquisition rate in less than 300 per year). From figure 1, it is clear that even if 45% of the Rio Grande flow were available for M&I at 160 gpcd, within 30 years, that would not be enough to sustain the projected regional population, since it would not even sustain the current population.

Water Conservation:

        Obviously, for a given volume of water, the lower the per capita water use, the larger the population that could be served. In that regard, conservation represents an important component of an overall water plan. In order to maximize the money and time expended on conservation, the most effective programs must be identified and expanded (if possible) and the ineffective ones eliminated. In that regard, two programs currently available through El Paso Water Utilities were evaluated: the toilet replacement program and the home audit program. The effectiveness of the toilet program was determined through a before and after study of participants and found to be highly effective. This is as expected, since toilets represents a significant fraction of the water used for residential purposes. The home audit program, however, was found to be not cost effective. While there was a decrease in water use in the homes that were audited, the decrease was small relative to the cost of the program.

Centralized vs On-Site Water & Wastewater Systems:

        Most people believe that a reasonable standard of living dictates that a house must be served by centralized water and wastewater systems. While such systems are considered the norm, in some cases, their cost might be so prohibitive that alternative on-site systems could be attractive. This is especially true for wastewater treatment systems, where the economically justifiable present cost per person at 100 gpcd is only $350.

Recommendations:

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