System input volume: annual
volume input to that part of the water supply
system to which the water balance calculation
relates.
Authorised consumption: annual
volume of metered and/or unmetered water taken
by registered customers, the water supplier and
others who are implicitly or explicitly authorised
to do so for residential, commercial and industrial
purposes. It includes water exported. Note that
this component may also include fire-fighting,
flushing, street cleaning, public fountains,
building water, etc. or some of these may be
unbilled and/or metered, depending on the water
utility’s policies.
Water losses: the difference
between System input volume and Authorised consumption.
Water losses can be considered as total volume
for the whole system or for partial systems such
as raw water mains, transmission and distribution.
Water losses consist of real losses and apparent
losses.
Real losses: physical water
losses from the pressurised system, up to the
point of customer metering. Physical losses after
the point of customer metering are excluded from
this definition of Real losses, but these can
be significant and may be worthy of separate
analysis. The annual volume of all types of leaks,
bursts and overflows depends on frequencies,
flow rates and average duration of individual
leaks.
Apparent losses: accounts for
theft or illegal use and all types of inaccuracies
associated with customer metering (the combined
effect of any under- and over-registration).
Non-revenue water: the difference
between System input volume and Billed authorised
consumption. Non-revenue water includes Real
losses, Apparent losses and Unbilled authorised
consumption.
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