What is the minimum and maximum water pressure for a house?
Summary (TL;DR)
Under AS/NZS 3500.1, the maximum static water pressure at any outlet within a building must not exceed 500 kPa. While the standard doesn't strictly define a universal minimum, most modern fixtures and appliances require a minimum working pressure of 50 kPa to 150 kPa to function correctly.
Water Pressure Limits (AS/NZS 3500.1)
Managing water pressure is crucial to protect plumbing fixtures, prevent water hammer, and ensure appliances work as designed.
The 500 kPa Maximum Limit
AS/NZS 3500.1 strictly states that the maximum static pressure at any outlet, within a building, other than a fire service outlet, shall not exceed 500 kPa (50 metres head).
If the mains pressure from the street exceeds 500 kPa, a Pressure Limiting Valve (PLV) or Pressure Reduction Valve (PRV) must be installed at the property boundary or before the first branch to the house.
Why? High pressure causes premature failure of tapware, burst flexi-hoses, blown hot water system relief valves, and severe water hammer.
Minimum Working Pressure
The plumbing code requires that the system is designed to provide adequate flow to all fixtures. While a strict numerical minimum isn't universally applied to the whole house, specific appliances dictate the minimums:
- Continuous flow gas hot water systems: Typically require 120-150 kPa minimum to ignite.
- Standard tapware/showers: Usually require at least 50 kPa for acceptable flow.
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