Thousands of houses in Adelaide receive high water pressure from the street main. People appreciate being able to pressure wash the car using just a garden hose but this convenience comes with nasty side effects both noisy and silent. The noisy one is water hammer and the silent one is the premature aging of hot water units. There’s also the problem of garden hoses that keep popping fittings, taps that are difficult to turn off and irrigation pipe that simply can’t handle it.

Since at least 2003, the National Plumbing Code (AS3500:2003) has stipulated that the water pressure in any building must not exceed 500kPa.

AS 3500.1 clause 3.3.4 Maximum water pressure Australian plumbing standards

AS 3500.1 clause 3.3.4 Maximum water pressure

Water hammer is a common complaint in Adelaide because many houses were built before the introduction of this regulation, and many areas are supplied with water at pressures well over 500kPa. I’ve heard of people buying water hammer arrestors and installing them on washing machine cocks and various other places to try to silence water hammer. Even if this helps the water hammer, it doesn’t deal with the high pressure (it often doesn’t do much to remedy the water hammer either).

A tap where the water pressure is 500kPa needs its valve wound onto the valve seat with a pressure of 500kPa in order to stop it from running. The same tap with a supply pressure of 800kPa needs 800kPa of closing force to stop it from running. This sounds like a simple matter of making the valve work 60% harder but the trouble is that things fail disproportionately faster as they are worked harder. Besides that, it’s a much nicer experience closing taps that don’t need to be wrenched off.

high water pressure

850kPa ouch!

This house in Windsor Gardens has 850kPa water pressure. My customer was complaining about not being able to stop her washing machine hoses from leaking. I wrenched them on and they still leaked because the plastic nuts just aren’t made to work with that much pressure.

The solution to high water pressure is a pressure reducing valve (NOT a pressure limiting valve – a PLV is a different type of device not suited for a water service supplying a whole house). A pressure reducing valve is essentially a pressure regulator. If your plumbing is good and your pressure is under 500kPa, you should have no water hammer, no stubborn taps and no horrible thumping when the washing machine starts and stops!

DN20 pressure reducing valve

A 20mm pressure reducing valve keeps the water pressure in the house under 500kPa