Date of Award
Master of Science (MS)
R. Scott Summers
Replacing potable water with graywater to flush toilets increases water efficiency in buildings. This study is an evaluation of water savings, environmental, economic, and policy impacts of graywater reuse systems as exemplified in a campus residence hall, Williams Village North, housing 500 students at the University of Colorado Boulder. Treatment of shower and sink drainage and recirculation for toilet flushing is estimated to reduce water use in the building by 20%, amounting to 3,300 m3/year (2.7 acre-feet/year). At municipal water and wastewater utility rates, the annual savings are around $6,000 and will not provide a reasonable return on investment for the capital cost of the dual plumbing and treatment systems. However, the graywater system was found to meet goals for other aspects of water sustainability, including physical, institutional, social, and environmental efficiency. Economic and technological efficiency were found to be net negative and net neutral, respectively, based on the unit price of water. Incorporation of the value of benefits such as greater drought resilience and deferred capital expenditures for expansion of municipal water supply and refined treatment system design produce greater economic and process efficiency. Constraints imposed by water rights held by the City of Boulder limit the application of indoor (non-consumptive) graywater reuse and add environmental impacts. Statutory recognition of residential graywater recirculation as a conservation practice, not a second use, is consistent with current agricultural and industrial recirculation practices, and would enable reduction of as much as 10% of city-wide residential water demand.
Spahr, Katie Marie, "The Challenges to Implementing Decentralized Water Reuse: a Greywater Recirculation Case Study in Boulder, Colorado" (2012). Civil Engineering Graduate Theses & Dissertations. 289.