Abstract
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.