Page 276 - The City and Guilds Textbook: Plumbing Book 1 for the Level 3 Apprenticeship (9189), Level 2 Technical Certificate (8202) and Level 2 Diploma (6035)

The City & Guilds Textbook: Plumbing Book 1

 Table 5.4 Advantages and disadvantages of the indirect system of cold water supply

Advantages Disadvantages
Reduced risk of water hammer and noise Supply pipe must be protected against
Constant low pressure supply reduces the backflow from cistern
risk and rate of leakage Risk of frost damage in the roof space
Suitable for supply to mixer fittings for vented Structural support is needed for the cistern
hot water supply Space taken up
Reserve supply of water available in case of Increased cost of installation
mains failure Reduced pressure at terminal fittings
Less risk of backflow – fewer fittings supplied
directly
Showers may be supplied at equal head of
pressure
Reduces demand on main at peak periods
Can be sized to give greater flow rate

Cold water systems in larger dwellings and
high-rise properties

For larger buildings (office blocks, factories, hotels, etc.), it is preferable for all
water, except drinking water, to be supplied indirectly via a protected storage
cistern, or cisterns.

Cold water systems in multi-storey buildings
KEY TERM In plumbing systems, the term multi-storey applies to buildings that are simply

Multi-storey: tall building too tall to be supplied totally using just the pressure of the water main. Because
that requires boosting of their design, these buildings have particular cold water system requirements
or pumping of the water that can be satisfied only by pumping or ‘boosting’ the cold water supply either
supply pressure given its in part or in total.
height.
Most cold water supplies that are delivered from the mains cold water supply
arrive at a building at a 3 to 7 bar pressure (30–70 metres head). A 30 m head is
equivalent to around eight storeys in height. When taking into account a two-
storey margin to allow for frictional losses, it becomes obvious that the height
of the building will often outstrip the head of pressure available. In some parts
of the UK, it is not unusual to find premises with pressures lower than 2 bars
and flow rates of below 15 litres/minute. In these cases, the water undertaker
should be consulted as to where supply pressures can be relied upon to ensure
the correct operation of the cold water system.
If the public supply is inadequate or the building too high, then the water supply
within the building must be boosted. There are several ways that this can be
achieved and these can be divided into ‘direct boosting’ systems, direct from
the cold water mains supply, and ‘indirect boosting’ systems from a break
cistern. Indirect systems are the most common as direct boosting systems
are often forbidden by water undertakers because they can reduce the mains
pressure available to other consumers in the locality and can increase the risk of
contamination by backflow. However, where insufficient water pressure exists
and the demand is below 0.2 litres/second, then drinking water may be boosted

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