Environmental Engineering Reference
In-Depth Information
relaxation and pleasure. Excepting the small children's evening bath routine, which
is practical (small children do not like showers), relaxing and fun for all, a bath is a
luxury, to be taken occasionally, when one is already suffi ciently clean, perhaps
with candlelight, possibly with just one alcoholic drink to hand, possibly with per-
fume and a partner.
Volume of Water
The canonical value, given in many places - for example,
Anglian Water (
undated
) - representing an average for the UK, is 80 l, and I have
confi rmed that this is about right. In addition, one can have a decent bath with some-
what less water and two can have a generous bath with the same amount.
Water Temperature
A bath thermometer has marks 'warm' at 37 °C and 'hot' at
41 °C, which is indeed the comfortable range. 'Warm' is better for the skin and in
addition produces signifi cantly less dampness. Note however that this range does
not apply to babies; Babycentre (
undated
) states that 37 °C is the safe maximum for
them.
Energy
Assuming that 80 l of water is used altogether; that the incoming mains
water is at the annual average temperature (12 °C); that the initial temperature is
37 °C, but subsequent topping up with hot makes the average 38 °C; that the boiler
(of condensing type) is 90% effi cient; and that 5% of the energy is lost in transmis-
sion from boiler to bath (an estimate), one fi nds that the energy needed is 2.8 kWh.
I have experimented with keeping the clean warm water in the bath for a second use
the next day. The temperature falls to the interior house temperature after 24 h. On
one occasion that was 19 °C (usually it would be rather warmer than this), and the
embodied bath energy recovered as space heating was 73% of the original. I took a
quick cool bath (the water was quite clean), and it was refreshing and nothing like
the shock of a cold (mains water temperature of 12 °C) bath. Rather it was more like
a quick dip in a heated swimming pool. Thus, a warm bath one morning and a cool
one the next make an energy and water effi cient, interesting and pleasurable
combination. One gets two baths for 80 l of water and only 0.75 kWh of energy.
This might however not always be compatible with general household activities and
other users, and it is not recommended during damp weather.
Time and Safety
When the bath is prepared, the energy and water have been taken.
Then it is the bather's turn to make the most of it. Enjoy a nice long soak, for which
the lower end of the quoted temperature range is better for the skin, with an occa-
sional top-up of hot water. A couple of safety points: by all means take a bath for
regeneration (that is what it is for) but not if you are dog-tired; a small amount of
alcohol may be nice but a large amount is not a good idea.
7.3
Basin/Bowl
A second reason why the mantra 'take a shower instead of a bath' is misleading is
that it leaves 'basin/bowl' unspoken. This method of washing would appear, from the
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