Page 273 - 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

6 SELECTING COLD WATER SYSTEMS

So far, we have looked at how water is collected, cleaned and distributed to
houses and industry. We will now move on to look at the cold water systems we
install in dwellings, their components, testing and maintenance.

Each dwelling should have a wholesome (often called ‘potable’, meaning
‘drinkable’) water supply, the most important place being at the kitchen sink. In
most domestic premises, it is likely that people will drink water from most of
the taps. This means that water to all taps should be connected to the mains
supply or come from a protected storage cistern.
Drinking water should also be provided in convenient locations in offices and
other buildings, especially where food is being eaten or prepared.

Domestic systems of cold water supply
There are two basic systems of cold water used in domestic dwellings:

1 the direct system of cold water
2 the indirect system of cold water.
The direct system of cold water supply

With this system, all cold water taps are fed direct from the mains supply. This
means that all taps are provided with a supply of drinking water. Storage is
required only for supplying cold water to the hot water cylinder via a 150-litre
cistern. A feed cistern will not be necessary if the hot water is supplied via an
instantaneous hot water heater or ‘combi’ boiler.
The direct system is the most commonly installed type of cold water system in
domestic properties because its installation is cost effective and there is usually
a relatively high-pressure supply available.

Pipe sizes for the direct system
Pipe size depends on the system design but, generally speaking:
● a 15 mm rising main will be large enough to supply most cold water
demands for a three- to four-bedroom house with all cold water outlets
being supplied in 15 mm, including the bath
● if a hot water storage vessel is to be installed, then a 28 mm cold feed pipe is
needed to the hot water storage vessel supplied from a 150-litre cold water
feed cistern in the roof space
● on larger installations, a 22 mm rising main may be required, but this will
depend on the water needs of the household.

If a combination boiler or instantaneous water heater is installed, then a 15 mm
mains cold water supply should, in most cases, be sufficient, depending upon
the supply pressure and flow rate.

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