An integrated energy, carbon, and economic analysis of reclaimed water use in Austin, Texas

As water supplies become increasingly strained, some municipalities have turned to reclaimed water as a potential low-carbon source to meet non-potable needs. Such reclaimed water - that is, wastewater effluent treated to appropriate quality standards - is not suitable for human consumption, but can be used for purposes such as irrigation and cooling that have limited human exposure. One reclaimed water distribution system of particular interest is at the University of Texas at Austin. This retrofit construction project receives treated effluent from the City of Austin Walnut Creek wastewater treatment plant distributed through a network of pipes ("purple pipe") using high service pumps and a reclaimed water tower. Depending on the embedded energy of existing water sources, existing levels of wastewater treatment, and the extent of a distribution network, water reuse can save energy and carbon emissions, at the expense of high up-front capital costs. Our analysis examines the embedded energy and carbon emissions in drinking water and reclaimed water for non-potable use at the University of Texas campus using EPANet modeling software and historical datasets. We complete our analysis by examining the overall economics of reclaimed water use, including capital and operating costs for a variety of amortization periods, financing costs, and externality costs using a levelized-cost of water methodology. This integrated analysis serves as the basis for developing principles of sustainable reclaimed water use.