37
HEALTH AND SANITATION
Greywater harvesting
techniques
Greywater has numerous uses, but how it is collected can
affect a number of different variables in its ultimate purpose.
A bucket is considered a low-
risk way to collect greywater.
By Water Research Commission
BUCKETING
A bucket may be used to manually harvest and use
greywater by, for example, collecting shower and laundry
water and using it for irrigation purposes (taking into
account the general rules for greywater harvesting). Such
an approach is generally considered to be low risk due
to the relatively small volumes of water and associated
contaminants. It is also unlikely to be undertaken during
wet weather (thereby reducing the risk of run-off). While
the use of buckets to harvest and reuse water is generally
considered low risk, there are several important rules
governing this use, in addition to the general rules for
harvesting:
• Make use of garden-friendly detergents low in
phosphorus, sodium, boron, and chloride.
• Spread the greywater around different areas in the
garden to prevent pooling.
• Monitor plant and soil response to greywater
irrigation — if your plants show signs of yellowing,
wilting or mottled colour, consider the above points
or stop applying greywater altogether. For example,
alternate irrigation with freshwater to leach out
salts if plants show symptoms of stress; apply
agricultural gypsum and compost to ameliorate
soils if infiltration rate decreases as a result of high
salt content.
• Consider applying a soil-wetting agent every sixth
months to assist in the absorption of greywater by
the soil (soils can become hydrophobic or water
repellent when they are dry for extended periods).
• Ensure that hands are properly washed, without fail,
after bucketing of greywater is finished.
GREYWATER DIVERSION DEVICES
The Government of Western Australia Department
of Health (DoHWA, 2011) provides comprehensive
information on options for greywater diversion. A
greywater diversion device (GDD) diverts greywater
without storage (apart from a temporary holding / surge
tank) or treatment; it incorporates a float- or hand-
activated switch or tap to divert the greywater to the
garden or the sewer. GDDs are the most commonly used
greywater reuse systems within sewered households in
South Africa. Greywater from a GDD should only be used
to irrigate gardens via subsurface irrigation, which means
that the irrigation should be buried at least 10cm below
the surface of soil or mulch. There are two common
types of GDDs, as follows:
• Gravity GDDs make use of gravity to provide
adequate pressure to move the water from the
house to the irrigation system. Such systems
require the house to be elevated or the garden to
slope away from the house.
• Pumped GDDs make use of a pump to convey the
water and provide pressure to irrigate the garden.
Such systems typically include a surge tank, which
holds the greywater until it has been used to
irrigate the garden.
GDDs are most appropriate for harvesting greywater
in single residential domestic properties where it is
possible to keep the greywater within the confines of the
property on which they are generated. The harvesting of
greywater using a GDD in commercial or multi-dwelling
properties should be managed by properly appointed and
trained personnel who can oversee the process in a safe
When using a
GDD to harvest
greywater, do not
leave the device
on continuously.
Treat it like
a garden tap
and only reuse
greywater when
the garden needs
watering.
Continued on page 39 >>
www.plumbingafrica.co.za
February 2019 Volume 24 I Number 12