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Tuesday, January 11, 2011

True Grit of Greywater

Thanks to Paul at JustWaterSavers USA for this tip. The greywater experts at Colorado State University just released this important interim report titled LONG-TERM STUDY ON LANDSCAPE IRRIGATION USING HOUSEHOLD GRAYWATER - EXPERIMENTAL STUDY sponsored by the Water Environment Research Foundation (WERF).

Why the study?

"The objective of this research project is to elucidate information on the fate and occurrence of graywater constituents and their potential impacts on soil quality, groundwater quality, and plant and human health as a result of its application for residential landscape irrigation".

What are the preliminary results?

"Much debate exists over whether graywater irrigation distribution systems should be submerged underground or if surface application of graywater is acceptable....In cases where top soil is shallow, application of graywater below the ground surface may actually result in resurfacing of graywater compared to surface application systems. The primary concern for surface application is potential human contact with pathogens in the top layer of the soil. While indicator organism numbers were highly variable among the three households in the top 0 – 6” of soil, numbers of indicator organisms were not consistently greater in areas irrigated with graywater compared to areas irrigated with freshwater in any sites tested, including those where graywater was surface applied. It is not possible to make comparisons about risk associated with surface drip irrigation as compared to submerged application of graywater based on pathogen indicator organism numbers measured for this study. Indicator organism numbers were not consistently greater in the top 0 – 6” of soil in samples collected from sites where graywater was applied to the soil surface as compared to a site where graywater irrigation emitters were buried below the ground surface".


A Gritty tale, indeed. More to come as the study progresses. Thanks for the great work on the environment, Rams! Thanks for the tip, Paul! 

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