Greywater Systems For Homes
Authors Sharvelle, Rosner et al. conduct a detailed analysis and assessment of the safety and environmental-related impacts of utilizing Greywater Systems For Homes in their study, “Long-Term Study on Landscape irrigation Using Household Greywater – Experimental Study.”
This study was an outgrowth of the increasing use of greywater systems as a means for providing residential landscape irrigation, despite the possibility that application of greywater in this manner may result in increased levels of pathogens in surface soil, negative impacts to soil quality, potential groundwater contamination, and/or other negative impacts to plant health or human health.
The study’s stated objective was to provide more information on the fate and occurrence of greywater chemical and microbiological constituents, and their potential impacts on soil quality, groundwater quality and plant and human health, as a basis for providing guidance on best recommended or safe practices for the operation of home greywater systems. Experimental studies were conducted in three parts; existing household greywater systems, new household greywater systems, and greenhouse studies.
Field study results on existing and new greywater systems for homes showed that most plants (19 out of 22 species evaluated) were healthy under long-term (more than 5 years) greywater irrigation. Only the avocado, lemon tree and Scotch pine species showed sensitivity to home greywater irrigation practices, as exhibited through reduced growth, leaf burning or reduced fruit production.
- While greywater irrigation was found to significantly increase sodium in households with systems in place for more than five years, these increases were not to levels as would trigger concerns for plant health or soil quality.
- While greywater irrigation did significantly increase surfactants in soil at households with new installations of greywater systems as well households with installations for more than 5 years, surfactant concentration did not continually increase with the duration of greywater irrigation.
- Greenhouse studies conducted by the researchers were inconclusive regarding the potential for greywater constituents to leach through soil and contaminate groundwater, but did find that the nitrogen present in greywater was in fact beneficial for plant growth.
Greywater and E. coli
Another area of concern for the researchers was the potential for greywater systems for homes to contaminate the environment with human-associated fecal organisms, including E. coli and enterococci.
Based on the data collected, however, the authors found no strong, consistent effect of greywater on estimates of E. coli or enterococci in soil. Contamination levels in the soil were inconsistent and depended on the household, sampling date and depth of soil sampled. In fact, because the above-described contaminants were detected in freshwater-irrigated soils, the study viewed this as an indication that sources in the environment other than greywater were responsible for fecal indicators.
Overall, the study found no major concerns that use of greywater systems for homes would be unsafe for human activities when they are installed and used according to best management practices.
The researchers did make clear that greywater does contain pathogens, and that actual human contact with greywater should be avoided. As a result, the study recommends that greywater systems for homes using drip irrigation have a protective layer of mulch above emitters.
The authors also point out that many states follow the best management practices established by the State of Arizona for the operation of residential greywater systems, and that some also require that irrigation systems utilizing greywater be submerged or underground. The researchers did make clear, however, that there was no indication that a submerged irrigation system resulted in fewer indicator organisms compared to surface irrigation systems. Having these systems under the ground’s surface simply makes it more difficult for humans and animals to come into contact with greywater.
In sum, this appears to be one of the most comprehensive studies to date on the health and safety impact of greywater systems for homes, and the authors seem to have carefully tackled the problem of how to assess the issues and analyze relevant data.
That being said, they are clear that certain questions remain unanswered and require additional research, including the impacts of antimicrobials in greywater irrigated soils, the use of mathematical models that could be developed and run under multiple soil conditions in assessing the fate of greywater constituents, and further research for assessing the risk associated with pathogens and viruses in greywater.