Page 291 - The City and Guilds Textbook: Plumbing Book 1 for the Level 3 Apprenticeship (9189), Level 2 Technical Certificate (8202) and Level 2 Diploma (6035)

Chapter 5 Cold water systems

Capacities of domestic cisterns INDUSTRY TIP

The British Standards no longer make reference to the minimum requirement
as to the amount of water that is stored in a cold water cistern. Instead, BS EN It is recommended that the
806 and BS 8558 recommend that each dwelling be taken separately, and the Water Efficiency Calculator be
amount of water calculated to suit the needs of the dwelling and its occupants. used to calculate the storage
requirements of a dwelling.
Kitchen sinks cannot be supplied from a protected cistern. Their supply must This can be found here: www.
come direct from the mains cold water supply. thewatercalculator.org.uk/
calculator.asp
General installation requirements for
domestic cisterns

Water is heavy. At 4°C it weighs 1 kg per litre, so 230 litres will weigh 230 kg –
almost a quarter of a tonne! From this, we can appreciate that a cistern full of
water will need adequate support, especially if placed in a roof space. Normal
practice would be to try to place the cistern over a load-bearing supporting
wall, as shown in Figure 5.44, but if this is not possible, then the platform (or
stillage) must be big enough to support the weight of the cistern and the water
it contains by spreading the load across the roof joists.

Cistern supported over the whole of its base.
The base should be at least 150 mm larger all
the way around than the base of the cistern

Cistern base to be made from At least 350 mm clearance for
moisture-resistant plywood or maintenance of the FOV and
tongued and grooved floorboard cistern cleaning

No insulation under cistern Cistern supported over
load-bearing wall

p Figure 5.44 Cistern shown positioned over a load-bearing supporting wall
The platform that the cistern sits on should be covered with 21 mm tongue and
groove boarding or moisture-resistant marine-grade plywood. The platform
should be at least as big as the base area of the cistern and, if possible, 150 mm
larger all the way around.
Access to the cistern, once it has been installed, is vital for cleaning, inspection
and maintenance. The minimum access allowance will depend on the size of the
cistern. For cisterns of less than 1000 litres, 350 mm must be allowed to permit
access to the float-operated valve before removal and replacement.

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