Direct on-site grey water reuse - an illicit or illustrious option?

Abstract: Grey water – wastewater from the bath, shower and washing machine – is available to all residential water users as a personal, on-site water resource (POSWAR). Despite contradicting reports on the value versus danger of on-site reuse, grey water constitutes a significant fraction (± 50%) of wastewater flow from a typical suburban home, where pharmaceuticals and personal care products (PPCPs) enter the water stream as soluble substances at grey-water producing points in a home. The work focuses on the impact of prolonged grey water reuse on soil chemistry and vegetation growth. An internet survey of 19 respondents suggests that garden watering is the predominant application for untreated, private on-site grey water reused in South African urban areas. As part of this research 15 different soil samples were collected from grey water use points and control points on 6 properties in the Western Cape, South Africa. The test results for acidity (pH), sodium (Na), phosphorous (P), electrical conductivity (EC) and nitrogen (N), show only Na to be consistently higher (on average by ±150%) in soil irrigated with grey water, compared to controls. However, grey water use does not appear to impact negatively on the vegetation growth in any of the sites inspected, despite one site reusing grey water for 20 years. All respondents to the survey reported that plants thrive when irrigated with grey water and could note no visible change in the soil, even after prolonged use. The same was confirmed during the six site visits. Extended research in the field is crucial to ensure the effective application of available water sources, including grey water, without compromising the health and safety of the urban environment