Several studies conducted by university students have shown that grey water encourages vigorous plant growth, and despite grey water use for periods of up to 20 years, no negative impact on the soil has been detected.
The thesis is entitled “DIRECT ON-SITE GREY WATER REUSE – AN ILLICIT OR ILLUSTRIOUS OPTION?” and is written by H.E. Jacobs and S. Van Staden
Quoted below is the conclusion they reached after testing soil quality from 15 different sources on 6 properties in the Western Cape.
“Soil samples from six households reusing grey water were analysed during this study. Standard soil analyses were conducted on 15 soil samples from grey water use points and control samples on each property. The only finding that was consistent throughout all the samples was that grey water reuse results in an increased sodium level – to a point substantially higher than that generally recommended for agricultural purposes, namely 70 mg/kg. However, garden vegetation and lawn grass seems to thrive when irrigated with grey water, despite the higher-than-recommended sodium content in the soil.”