HEALTH AND SANITATION
46
A complete greywater
harvesting system installed at
the University of Colorado, US.
Appropriate uses
for greywater
On-site residential greywater reuse is a potentially
promising alternative water resource if managed
correctly — particularly in low-density, high-income
areas where health concerns are less pronounced.
By Water Research Commission
Reuse schemes need to be simple and economical,
whilst at the same time protecting the environment
and public health. Greywater reuse has the potential
to result in potable water savings through offsetting
the use of such water for non-potable purposes.
From a ‘fit-for-purpose’ perspective, greywater is most
appropriate for activities such as toilet flushing and garden
watering / irrigation, where human contact is limited.
However, even in these cases, there is potential for health
risks; for example, in the context of toilet flushing, water
droplets are aerosolised and land on nearby surfaces or
can be dispersed into the air. The pathogens are then
transferred through hand-to-mouth contact after toilet use,
if thorough hand-washing is not observed.
Similarly, it is strongly suggested by many international
authors that untreated greywater should only be used for
subsurface irrigation purposes, to limit the risks involved.
In addition to this, discolouration, odours, and negative
perceptions about wastewater can also present barriers
to its use as an alternative water resource.
Depending on the availability of potable water resources
in a specific area, greywater may also be used for
small-scale irrigation — with appropriate risk prevention
November 2018 Volume 24 I Number 9
barriers in place. The complexity of installing and
managing these greywater systems presents a challenge
for broad-scale adoption within urban catchments.
Greywater harvesting is usually heavily decentralised,
taking place within the boundaries of individual
properties, and the responsibility of managing these
systems falls on the property owners. However,
in densely populated urban areas and/or informal
settlements, management of greywater jointly with
other domestic wastewater in a combined collection
/ treatment system such as constructed wetlands
(that is, a centralised system) may be technically and
economically more feasible.
In this regard, proactive participation and involvement
from the involved ‘community’ is essential for the
effective implementation of greywater systems. There
are likely to be significant differences between the way
greywater is used and managed in serviced and un-
serviced settlements.
Whether greywater reuse is intended or not, particularly
in areas that are un-serviced (and rural or peri-urban
areas), control and/or risk aversion measures are
required to be put in place to ensure safe disposal of
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