Internal services

8.1.4Cold water storage

Cold water service shall be provided in accordance with statutory requirements and be adequate.

Cold water storage should be provided with suitable capacity and include primary feed cisterns where indirect water heating systems are installed. Cold water storage should be provided:

  • to supply an open vented hot water storage system (where required by the water supplier)
  • to supply cold water outlets (where not connected to the mains supply).

Cisterns should:

  • be accessible for inspection and maintenance
  • be protected by a rigid close-fitting cover (non-airtight) that also excludes light and insects
  • have holes neatly formed with a cutter in the positions shown in the design
  • be suitably supported.

BS 6700 provides the following recommendations:

  • Storage capacity for small homes – only cold water fittings – 100-150L.
  • Storage capacity for small homes – supplying hot and cold outlets – 200-300L.
  • Storage capacity for larger homes – 100L per bedroom.

Warning and overflow pipes:

  • should be provided at each cold water cistern, to a suitable external discharge, unless permitted by water regulations where it may be internal if it is conspicuous
  • should be adequately sized (19mm minimum)
  • should be situated 25mm from the shut-off water level in the cistern
  • may dip below the water level in accordance with water regulations, terminate vertically downwards or be fitted with a horizontal tee where it discharges.

The cistern bottom should be continuously supported by materials such as:

  • softwood boarding
  • marine plywood
  • chipboard type P5 to BS EN 312
  • oriented strand board type OSB3 to BS EN 300, laid with the stronger axis (as marked on board) at right angles to the bearers.

Access should:

  • be provided to the main roof space and voids that contain cisterns and tanks, etc. (not required to roof spaces containing only water pipes)
  • be via an opening (access hatch) with a minimum width of 520mm in each direction
  • not be located directly over stairs or in other hazardous locations
  • include a minimum 1m² platform located for maintenance purposes
  • include securely fixed boarded walkways between the opening and the cistern or other permanent equipment (boarding should be securely fixed without compressing the insulation).