58
HEALTH AND SANITATION
Rainwater tanks are not
‘set and forget’ systems
By Eamonn Ryan
As a growing number of South African households install
rainwater tanks as a primary water source, it’s important to raise
awareness that these tanks are not a set and forget system.
In 2016, the Water Research Commission and
Department of Agriculture, Forestry and Fisheries
released a report on the health and efficiency of
rooftop rainwater harvesting, titled ‘Microbial Quality
of Rooftop Rainwater’, a report to the prevalence of
faecal indicators.
“A total of 365 water samples from three boreholes (5.1%),
five ground harvested rainwater tanks (4.1%), five rivers
(10%), 80 roof-harvested rainwater tanks (79.7%) and one
spring (1%) were collected. Sample collection was further
divided into early (October to December) and late (January to
March) rain season. Water quality was evaluated based on
E. coli, coliforms and enterococci detection. In RRWH
E. coli were detected in 44.1% of the samples, Enterococcus
in 57.9% and faecal coliforms in 95.7% of the samples.
The most prevalent concentration of E. coli (29.1%) and
enterococci (19.5%) were within 1-10 cfu/100 mℓ, whereas
those for faecal coliforms (36.6%) were within 100-1000
cfu/100 mℓ. Evaluation of the microbial quality of river water
used by the villagers as an alternative water source revealed
that 79% tested positive for Enterococcus, 39% for E. coli,
and all samples for faecal coliforms.
The majority of the samples that tested positive for
Enterococcus (32%) and Escherichia coli (E. coli) (16%) had
a concentration of 10-100 cfu/100 mℓ. However, the majority
of the concentrations for faecal coliforms detected (48%)
were of concentrations greater than 1000 cfu/100 mℓ.”
This warns that many rainwater tanks contain unsafe
drinking water caused by a lack of maintenance. While it is
well known that rainwater collected and stored in domestic
rainwater tanks contains some harmless micro-organisms,
this research found that E. coli is becoming more common in
rainwater tanks in South Africa.
“Most of the contaminant risks regarding rainwater tanks
are due to maintenance issues, but traps or pooling in
stormwater lines also have the capacity to compromise
the quality of rainwater,” says Philip Doust, managing
director of Doust Plumbing Products. The company, based
in Perth, Australia, has developed a pre-tank filter known as
Rainwatch (see the Victoria Yards project in Plumbing Africa,
March issue) which has recently been launched in South
Africa. Rainwatch provided the pre-tank filter for the fixed,
off-grid toilet facility at Victoria Yards, which also employs
Enviro Loo sanitary technology, and is built by construction
technology company BOXA and its partners.
Philip Doust (centre), managing director of Doust Plumbing Products with some happy
customers.
www.plumbingafrica.co.za
@plumbingonline
@plumbingonline
Grant Oldfield, director of Northstar Development, the sole
agent for Africa of the Rainwatch filter, says, “The main
purpose of the device is to cost-effectively improve the
quality of harvested rainwater and reduce the build-up
of debris, contaminants and sediments in the storage
container. It is primarily used in residential rainwater
storage applications in Australia, Thailand, Vietnam and now
South Africa. Multiple units can be used to accommodate
larger roofs.
@PlumbingAfricaOnline
April 2020 Volume 26 I Number 02