Colorado State University Professors Explore Graywater Irrigation as Potential Water Conservation Tool

Note to Editors: A photo of the CSU graywater team is available with the news release at

Graywater – nonpotable water from showers, handwash sinks and laundry – is used for residential landscape irrigation in a number of states in the Southwest; however, little is known about long-term effects of this practice, according to Colorado State University civil engineers.

Sybil Sharvelle and Larry Roesner, professors with the Urban Water Center in Colorado State’s College of Engineering, are in the first year of a three-year $370,000 graywater study awarded by the Water Environment Research Foundation to investigate the effects of using household graywater for residential landscape irrigation. They are sampling soil, plants, and water at homes with graywater systems in California, Arizona, Texas and Colorado. Four of the homes have graywater systems that have been in place for more than five years, and four additional homes will have new systems installed before spring of 2009.

Three homes with systems in place for more than 5 years – in Colorado, California and Texas – have been tested to date.

"We are assessing plant health, soil chemistry and microorganisms in graywater irrigation areas and comparing the findings with samples taken in the same yard where similar vegetation exists that is irrigated with city water,"  Sharvelle said. "You can’t just assume that if a plant looks good now, that it has long-term viability. By applying scientific analyses of plant health, soil quality and microbial populations, we will be able to shed better light on whether it is safe to irrigate landscape for long periods with graywater."

For the study, the team picked states where governments have taken interest in graywater systems or where regulatory processes have been established. California, for example, has detailed regulations for graywater irrigation systems, targeted at minimizing human interaction with graywater due to concerns about pathogens and graywater chemical constituents such as surfactants – a common ingredient in soap. Arizona has a permitting process that tracks graywater systems through the state’s Department of Environmental Quality.

Colorado is currently working to develop regulations for outdoor graywater reuse.

"This study will provide scientifically sound information for assessing the safety of graywater reuse in household irrigation," said Drew McAvoy, environmental engineer for Procter & Gamble and chair of the steering team overseeing this project. "Results from this study will also help consumer product manufacturers determine appropriate product use and disposal recommendations for graywater reuse systems."

"Regulators have not had a good set of scientific data to make science-based decisions, which is why we’re doing this study," said Roesner, the Harold H. Short endowed chair for urban water infrastructure systems at Colorado State. "These are all states where drought and water quality are serious issues."

Also working on the project are Yaling Qian in Colorado State’s Department of Horticulture and Landscape Architecture and Mary Stromberger in the Department of Soil and Crop Sciences in the College of Agricultural Sciences who are evaluating soils and plant health.

The study is one of four projects that Roesner and Sharvelle are leading on campus. The team also is working with the CSU Department of Facilities Management on several projects involving campus facilities including:

-Construction and monitoring of a wetlands treatment system for graywater at the Atmospheric Chemistry building on the Foothills campus. Students planted bull rushes and cattails last summer that, so far, are removing nearly all of the pathogen indicator organisms in sink and shower water, Sharvelle said. Researchers are also hauling shower and laundry water from a university residence hall to the Foothills campus to increase the quantity of water treated.

-Installing an anaerobic digester at the Atmospheric Chemistry building to treat toilet water or "blackwater" and test it as a source of renewable energy. Anaerobic processes generate methane, which can generate electricity.

-Plumbing one wing of the new residence hall, under construction, for complete capture of graywater from sinks, showers and laundry water; in addition, water supply lines to toilets are being plumbed to use either domestic water, or non-potable water (irrigation water or conditioned graywater) for toilet flushing. Studies by Sharvelle and Roesner will determine what level of treatment of graywater is required to make it suitable for toilet flushing. They are working with Water Legacy, a Colorado manufacturer of graywater treatment systems.