Options to consider include:

• gravity (low pressure) or mains pressure supply
• water supply layout considerations
• water storage tanks
• water for flushing.

Gravity or mains pressure supply

Gravity supply:

• A low pressure system operating from a water storage tank.
• Water source is at a higher elevation than the supply outlets.
• Requires few (if any) pumps, valves or controls.

Mains pressure supply:

• High pressure supplied from the mains water supply.
• Requires a system of valves to control water pressure and temperature.

Water supply layout considerations

When planning a water supply layout, the following must be considered:

• Supply source – Is the source on-site or mains supply?
• Pipe runs and lengths – Keep pipe runs as short as possible. Pass pipes close to fixtures to minimise the number of branches and unnecessary elbows, tees and joints, as these result in frictional losses.
• Point of entry into the building – This should be into a utility space such as garage/laundry and include an accessible isolating valve, line strainer and pressure limiting valve (if required).
• Water heating system – Locate centrally to reduce the length of pipe runs to fixtures because longer pipe runs require more water to be drawn off before hot water is discharged. Install a separate point-of-use water heater for fixtures that are more than 10 m from the main water heater.
• Noise prevention – Avoid running pipes over or near bedrooms and living areas.

Water storage tanks

Cold water storage to provide adequate personal hygiene facilities may be required in buildings where people are physically confined (Community Care classification).

Water storage tanks may also be required in other situations to provide:

• a reserve water supply
• adequate pressure to a supply system
• an air break.

Installation requirements for cold water storage (header) tank for residential purposes include:

• adequate support
• seismic restraint
• provision of an overflow pipe (to be visible)
• a safe tray placed under the tank to prevent damage by leakage or overflow (NZBC G12/AS1 only)
• covers to openings if a potable water supply
• access for inspection and maintenance
• sufficient height above the highest outlet.

Water for flushing

Water for flushing must be provided to:

• toilet pans
• urinals
• fixtures used in hospitals such as bed pan washers, flushing sinks, slop hoppers and flushing floor waste gullies.

Water for flushing must be provided from:

• a storage cistern
• a flushing valve.

A flushing valve may be supplied from a storage tank, in which case it must be isolated from the potable water supply, or from the mains supply system, in which case a backflow prevention device must be incorporated.