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HEALTH AND SANITATION
Development of resource
guidelines for rainwater
harvesting
By Water Research Commission
South Africa has to prioritise from the mix of available water
supply options to meet the huge water demands and for equitable
allocation to enable development and economic growth.
The country is actively pursuing alternative water
sources, which include water reuse; desalination;
groundwater utilisation; water conservation and
water demand management measures; recovering
water from acid mine drainage; and the import of
water-intensive goods. Rainwater harvesting (RWH)
is an age-old proven practice that could also be
undertaken and has regained popularity.
An enabling environment and government support
are necessary for spreading the concept and the
implementation of RWH systems on a larger scale.
Despite benefiting from the support of several national
government departments, RWH is not being utilised to
its full potential. The lack of clarity of the water-related
legislation and the absence of a national umbrella body
that coordinates the implementation of the practice,
are preventing the effective multisector involvement
and promotion of RWH. There should therefore be
a deliberate focus on RWH knowledge sharing and
capacity building, along with the creation of an enabling
environment, and the development and enhancement of
suitable frameworks, policies, and legislation.
RWH is used for various purposes, depending on
where the systems are implemented. In urban areas,
it augments municipal supply, while in rural areas it is
often either the sole or the best water supply source
available. National studies on the physio-chemical and
microbial quality of the water harvested indicate that it is
often below gazetted water quality standards. The main
source of contamination is the wash-off into the storage
tank of airborne pathogens and organic matters from the
catchment surface. Thus, some sort of pre- and/or post-
water treatment is required. The level and the complexity
of such treatment are governed by the intended use of
the water. RWH systems of different geographical areas
October 2017 Volume 23 I Number 8
are subjected to different types of contaminants and,
therefore, require different water treatment. To maximise
effectiveness, a multi-barrier approach where more
than one method of treatment (such as sedimentation,
filtration, and disinfection) are used is recommended.
An analysis of the type of contaminants found in
harvested rainwater in different geographical areas of
South Africa, exploring existing and upcoming treatment
methods, and quantitative risk assessments to estimate
health risks associated with the use of polluted harvested
rainwater is required. In addition, guidance on how
RWH systems should be implemented and training
of households on the appropriate use the harvested
rainwater, must be provided.
There is the misguided belief that back-of-the-envelope
calculations are sufficient to size RWH systems. An
additional R2 000 (the price difference between a 5m 3 and
a 2.5m 3 Jojo tank) might not overburden the budget of a
middle-income urban household, but it has a major impact
on the budget of any government department that plans
on installing thousands of systems across the country.
Literature indicates that several models to help
determine sizing RWH systems have been developed.
Unfortunately, for one reason or another, most of those
models are unavailable to the public. Moreover, most of
the few available models have not been validated against
observed data. The lack of observed data with which to
both run and to validate the models remains the main
impediment. As a consequence, it is difficult to quantify
with a reasonable degree of confidence, water savings
using rainwater tanks.
The most important question to pose is, “What will the
water be used for?” That not only determines to which
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