Green Economy Journal Issue 39

Water Management
Urban Water
Photos by JG Afrika
Management
BY BENJAMIN BIGGS, CIVIL ENGINEER, JG AFRIKA
The uninterrupted availability for clean water for many industries is a prerequisite
for operations. To what extent are companies in South Africa at risk of interruptions
in the supply of water, or the supply of quality water of the required standard?
Cape Town’s Drought of the Century forever changed the City’s
urban water management landscape. Declared as a disaster
area in May 2017, the City of Cape Town faced severe level 6b
water restrictions – up to 50 litres per person per day. Residents and
businesses alike experienced considerable water tariff increases. The
possibility of Day Zero threatened business continuity and precipitated
a necessary discussion on the value of water as a resource.
Cape Town’s water comes almost entirely from surface water resources
(i.e. rainfall run-off into dams), which is captured and stored in six major
reservoirs around the city. Supply dependence on surface water resources
can reduce supply resilience to climatic shocks, such as drought.
Considering tariff increases and supply stresses; reducing domestic and
commercial water demand; as well as associated water costs has become
important for industries, homeowners and businesses. Consumption in
toilets, taps, showers and irrigation typically comprise 60-80% of potable
use in domestic and commercial areas and targeting these water uses
became the focus for demand reduction strategies.
Interestingly, business continuity, rather than savings on utility bills,
became a primary motivation for de-centralised alternative supply.
Water Sensitive Design (WSD)
WSD is a globally accepted concept that addresses the limitations of
conventional urban water management. It integrates all aspects of the
water cycle with urban design to provide economic, environmental and
social (sustainability) benefits. These principles form a framework through
which sustainable water management can be achieved.
Fit-for-purpose
‘Fit-for-purpose’ use is important when selecting a suitable alternative
supply for a local site. Not all water supply needs to be a potable (drinking)
standard. The application, available quantities and associated risk should
determine the level of treatment incorporated. Non-potable use within
buildings often necessitates altering plumbing networks – a process that
is the easiest to incorporate during the design stage.
Source diversification
Source diversification provides resilience against climatic shocks, such
as drought. This requires identifying and matching suitable alternative
sources with appropriate application(s).
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Alternative supply
CASE STUDY: STELLENBOSCH UNIVERSITY
GREYWATER SYSTEM
These principles were applied in the design and operation of a greywater
system at Stellenbosch University (SUN). One of the largest of its kind in
Africa and a Water Category winner at the 2019 South African Institution of
Civil Engineering (SAICE) Western Cape Regional Awards, the system was
designed to provide fit-for-purpose water for SUN.
Once both installation phases have been completed, the network will
flush over 1 300 toilets used by about 25 000 university students to meet
a significant portion of campus water supply and supplement campus
irrigation. During term time, up to 75 m 3 /day of greywater can be treated
and reused (Phase 1). This capacity could be increased to between 150 and
200 m 3 /day after Phase 2.
Eight representative buildings on campus were assessed and modelled.
Water characteristics from each type were then extrapolated across
campus to other similar buildings and calibrated against utility data to
develop a comprehensive campus water balance. Interventions focused
on the top 40 users, comprising 80% of total water demand and the
WSD principles were then applied according to the Water-Management
Hierarchy. Notably, campus interventions introduced as part of the first
“reduce” stage of the Water-Management Hierarchy decreased potable
water use during the drought by more than 50%.
Alternative water supplies were then investigated. The Water Masterplan
identified treated greywater reuse on campus as a viable alternative
Photo by JG Afrika
SUN greywater treatment plant and storage facility.
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