Abstract:
Energy consumption in water supply and
distribution networks represents 7% of
the world’s consumption of energy. According to the Key
World Energy Statistics published by the
International Energy Agency,
the water sector accounted for 820 TWh
of global electricity consumption in 2014.
This amounts to 70 million tons of oil
equivalent (MTOE). These Key World
Energy Statistics summarise the average
electricity consumption for all processes
within the potable water supply chain, from
abstraction through treatment to distribution.
Incorporating these global averages,
and by using average water consumption
for South African metros as reported by
the Department of Water and Sanitation and the Eskom average electricity
rate, we can approximate
the average annual electrical cost for water treatment and distribution of a metropolitan
municipality with a population
of 3 million to R166 million. According to
the GreenCape Market Intelligence Report
on Water for 2017, South
African municipalities currently use about
4 500 million m³/year of water, of which
37% is non-revenue water. On this basis,
on average, a metropolitan municipality with a population of 3 million loses around
180 million m³ of potable water per year,
which amounts to a cost of roughly
R60 million per year on the electrical cost
for the treatment and distribution of nonrevenue
water. This R60 million
cost could be recovered to some extent
through energy recovery using hydro turbines
or energy recovery turbines (ERTs).
Subsequent savings on water losses and
the overall energy cost of the system are
also present, but should be quantified on a
site-specific level, as these vary according
to location and system configuration. The
energy recovery benefit figures change with
various factors, such as the topography,
treatment processes and distribution
lengths. The City of Tshwane has a population
of roughly 2.9 million, but its energy
cost of water would be higher due to the
higher pumping cost of water procured
through Rand Water and pumped from the lower-lying Vaal Dam.
