Grey Water Use as a Water Management Option in Las Vegas, Nevada

Southern Nevada, located in the southwestern region of the United States has forecasted increases in water demands and limited water resources. Incentives have been implemented by the Southern Nevada Water Authority (SNWA) to encourage residents to reduce residential outdoor use. As the residential outdoor use campaign becomes exhausted, additional policies should be considered. The idea of grey water reuse to reduce fresh water residential outdoor use is investigated. A dynamic simulation model using system dynamics modeling approach is developed. A policy requiring all future development (beginning in the year 2008) in southern Nevada to divert a portion of used indoor water to supplement outdoor use is evaluated. This policy reduces the water withdrawn from Lake Mead resulting in reduction in back and forth transport of water to and from Lake Mead, but it also reduces the return-flow credits. Energy consumption (pumping and treating) decreases, energy extraction (in the Las Vegas Wash) decreases, infrastructure expansion rates decrease for both potable and wastewater facilities, and losses due to evapotranspiration decrease because less water is being exposed to the atmosphere. The model shows that if 40 gpcd of indoor water used (grey water) is diverted for outdoors use, 2.28 10⁴ million gallons per year (70,000 acre feet) of water savings can be achieved by the year 2035 and $6.3 million per year pumping costs can be saved. To address environmental and public health concerns purple piping for grey water reuse systems should be used and monitoring wells should be installed.