A quick shower uses a third of the water of a
bath, but power showers can use more water than a
bath in less than five minutes.
How much water can we save?
In the typical UK household, bathing
accounts for about 20 per cent of annual water use.
Showers are usually seen as a water-saving
alternative to baths, since they use about a third
of the water and energy of an ordinary bath. Recent
trends with "power showers", however, have increased
flow rates to the point where water use for a single
gainsborough shower can more than equal that of a
There is no agreed definition of a
water-efficient shower. Unlike washing machines or
WCs that use fixed volumes of water per cycle or
flush, shower water use depends very much on user
behaviour and water pressure levels.
The choice of mixer valve will influence
water use for showering. Simple hot and cold tap
controls require both taps to be adjusted with an
infinite number of possible combinations in order to
achieve the desired flow and temperature. As this
must be done by feel, the valves will have to be
adjusted as the hot water starts to reach the mixer
and there is always a risk of scalding. Turning off
the flow to apply shampoo would require a repeat
performance, so the water tends to be left running.
Thermostatic mixers have a calibrated dial, allowing
the temperature to be set from experience. The flow
is adjusted with a separate control so that reducing
or interrupting the flow, for example to apply
shampoo, is a simple matter.
Trials at the Building Research Establishment (BRE)
found that most people find flow rates of less than
three litres per minute unacceptable and are
satisfied with a flow rate of 10 litres per minute.
Sufficient flow is required to provide adequate
wetting, to rinse off soapsuds and to provide
sufficient warmth to the bather. The design of
showerhead will influence all these functions.
"Water-saver" showerheads usually work by
creating finer drops or by introducing air, rather
like the tap aerators. Typically, such showerheads
require a pressure of at least one bar (100 Kpa),
which is available from mains pressure systems but
not from gravity-feed hot water systems without a
pump. These water-saver showers typically work at a
flow rate of between four and nine litres per
minute, and the effect is usually perceived as a
"power shower" but with perhaps half the flow rate.
Apart from the need for sufficient water pressure,
the main criticism from some users of these showers
is the "cold feet" effect of the faster cooling of
the fine droplets. Water-saver showerheads and
restrictors should not be used with electrically
heater showers without the consent of the
manufacturer, as this could be dangerous.