If a premises has any form of mains water supply, then the water fittings regulations in England, Wales and Northern Ireland, byelaws in Scotland, apply.
These legal requirements play an important role in protecting public health and safeguarding water supplies. Their purpose includes preventing the contamination and waste of water supplied by a water undertaker once it has entered a customer’s plumbing system.
A cold water storage cistern may be installed for various reasons including:
To provide backflow protection
To provide a reserve supply in the event of any disruption to the incoming cold water supply
To reduce the maximum demand on the cold water supply
To reduce the supply pressure
In many cases the local water undertaker will need to be given advanced notice of the proposed installation of any cold water cistern. This is an important simple and essential check to minimise the risk to water supplies.
Even if a cold water storage cistern is to be used solely for storing water for drinking, washing, bathing or other purposes requiring it to be wholesome, as a condition of consent it is likely the local water supplier will require backflow protection to be installed. This is typically achieved by suitable air gap arrangement; in some circumstances a double check valve may also be required.
Please note: as well as providing storage a cold water storage cistern may be providing backflow protection for installations downstream. For this reason, they should not be removed without firstly consulting with the local water undertaker.
All components making up and used within a cold water storage cistern must be of an appropriate quality and standard
All non-metallic materials in contact with water, including any surface where condensate forms, must conform with the current version of BS 6920 (or an equivalent).
Cisterns should be watertight and where appropriate lined or coated with suitable impermeable materials.
In addition to an inlet, outlet, overflow pipe and warning arrangement a cistern should have a rigid close fitting and securely fixed lid or cover. Cisterns, and their lids, should be made of materials which do not shatter or fragment when broken.
Where the water stored in a cistern has to remain wholesome, it is important to minimise the risk of contamination. Key to this is making sure the water is stored for as short a period as possible.
This is achieved through a combination of design and maintenance features, correctly sizing the cistern to ensure the regular turnover of the stored water and avoiding stagnation as well as any deterioration of water quality.
Factors which should be considered when sizing a cistern include occupancy (intended and actual) and usage. Suggestions for storage capacity are given in BS EN 806-2.
Factors to consider when deciding where and how cold water storage cisterns are installed include but are not limited to:
whether the distributing pipework (system) is pumped or supplied by gravity
the need to allow for ease of access for maintenance
inspection (both internally and externally)
cleaning requirements
environmental factors which might affect water quality such as excessive heat gain or the likelihood of flooding.
Float operated valves and other controls should be readily accessible. There should be sufficient clearance to allow for inspection, cleaning of internal surfaces and maintenance.
Cisterns with a capacity greater than 1,000 litres should be capable of being inspected and cleansed without having to be wholly uncovered.
To avoid distortion cold water storage cisterns should be adequately supported. Advice on how to do this can be found in Part G of the Building Regulations.
Please note: In many cases the local water undertaker will need to be given advanced notice of the proposed installation of any cold water cistern. This is an important simple and essential check to minimise the risk to water supplies.
Due to concerns about water stagnation, which might cause the quality of the water to deteriorate, the installation of inter-linked storage cisterns should be avoided wherever possible.
Where it is unavoidable, the number of inter-linked cisterns should be minimised. To minimise the risk of stagnation:
The storage volume should be kept to a minimum
Cisterns should be connected in parallel
Any demand should create water flow throughout each cistern
Inlet and outlets should be installed at opposite ends of the cistern
Delayed action float valves should be used
Metering of inlets may assist with balancing of turnover
An inlet valve must be fitted. This should be securely and rigidly fixed and must shut off the flow at a set level within the cistern. Typically, this level is a minimum of 25 mm below the overflow but should be increased to a minimum of 50 mm if there is no warning pipe. Where a float operated valve is to be used, this must be capable of being adjusted to ensure that the inlet valve closes at a defined level.
Where the inlet forms part of an air gap arrangement intended to prevent backflow, the inlet valve should not come into contact with the contents of the cistern as a result of splashing or foaming. If this occurs the inlet valve should be adjusted to increase the air gap.
Float operated valves are generally, but not always used for controlling the flow of water into a cistern. Electrically or pneumatically operated valves are also an acceptable form of valve for controlling the inlet flow. In all cases the method of installation must be suitable for the specific installation and comply with all aspects of the appropriate water fittings regulations/byelaws.
Transient pressure increases or surges (water hammer) may be caused by the rapid closure of valves, resulting in a sudden stop or change of water flow. To keep pressure surges within reasonable limits and prevent damage to water fittings hydro-pneumatic accumulators, surge arrestors or pressure reducing valve can be installed.
In addition to any backflow protection required by the local water undertaker a servicing valve must be installed on the inlet adjacent to the cistern and outlet to facilitate maintenance and minimise waste.
To encourage mixing and prevent areas of stagnation or ‘short circuiting’ within the cistern where practical the cistern inlet and outlet should be on opposite sides of an appropriately sized cistern. Where multiple cisterns are linked; inlets and outlets need to be carefully balanced to promote a good turnover of water in each cistern.
Where practicable all outlets from a storage cistern should be located at the bottom of the cistern and to encourage mixing and prevent areas of stagnation or ‘short circuiting’ within the cistern on the opposite side to the inlet.
All outlets from cold water storage cisterns, except vent pipes, overflow pipes and warning pipes, should be fitted with a servicing valve as close to the cistern as is reasonably practicable.
Every cold water storage cistern must be fitted with an overflow pipe.
To help minimise waste a suitable means of warning of an impending overflow must also be installed. A warning pipe is commonly used for this purpose, but with the local water undertaker’s agreement alternatives may be fitted. Although usually separate a combined overflow/warning pipe may be accepted on cisterns with a capacity of 1,000 litres or less.
Overflow and warning pipes must be positioned so as to exclude light and insects. A screen with a mesh size no greater than 0.65 mm (opening) is typically used to prevent the ingress of insects and other foreign bodies. If an insect screen is installed it should be vertically and removable.
Overflow and warning pipes should be installed on a downward inclined plane and not discharge into any other cistern.
The discharge from the overflow and/or warning pipe should be safe and conspicuous. If discharging to drain a visible air brake, giving fluid category 5 backflow protection in the form of an air break to drain conforming to the design specification given in EN 1717 must be installed.
If a common warning pipe is used the location of the cistern overflowing must be readily identifiable. A warning/overflow pipe should be at least 19 mm (internal diameter) and capable of accommodating all possible flow rates i.e. the maximum inflow under fault conditions. The effect of any screen on the nominal flow capacity must be taken into account when determining the size of an overflow.
To minimise the risk of contamination resulting from microbial growth and wastage due to taps left to run, cold water storage and distribution systems should be designed and installed to maintain a temperature not exceeding 20oC.
Plumbing systems should be designed and installed to ensure there is regular flow through.
To prevent undue warming, it is good practice to insulate both hot and cold water pipework. Unless it is adequately protected water fittings should not be installed where it could be exposed to heat sources, such as other services or sunlight.
For further information please refer to BS EN 806, BS 8558 and HSE Legionella ACOP.
When designing a compliant plumbing system a number of factors need to be considered, including but not limited to:
Avoiding the risk of contamination or damage resulting from the environment in which the system is to be installed or due to the design itself.
The required and attainable supply pressure and other operational parameters
User expectations and whether these are achievable
Suitability of water fittings for use
Providing appropriate, adequate backflow protection.
Water efficiency
Limiting waste.
Useful sources of information include BS EN 806 and BS 8558
Regulations & Byelaws which apply include but are not limited to:
Relevant guidance includes but is not limited to:
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