Maximum pressure for municipality water connection

By Vollie Brink, Pr Eng

An engineer friend phoned and asked me, “What is the maximum pressure that the municipality’s water connection is supposed to be?”

My answer was, “900kPa as per the national model by-laws, but these model by-laws also state that the water connection is provided under three conditions, which are: no guarantee of water, no guarantee of pressure, and no guarantee of quality, and it is taken up in the local water by-laws of the municipalities.”

My engineer friend also complained that the municipality worked on the water supply piping near his house and when they re-opened the valves too quickly, it caused massive water hammer and a surge of high pressure — above 900kPa — at his house.

I have received numerous complaints about very high municipal water pressures during night-time and in some cases, the pressure went up to 20 bar, causing damage.

Although the municipality is not allowed to give you water at a higher pressure than 900kPa, they are ‘covered’ by the fact that they do not have to guarantee a specific pressure.

On the one hand it is a problem, but on the other hand one must be thankful to have water, even at a non-guaranteed pressure.

I had a case where a municipality worked on the water supply piping during the night and they raised the pressure to be able to supply water. When the work was done, they opened the valves too quickly and a huge wave of water caused about 2km of piping to be pulled off the slab in the basement. Fortunately, it was night-time and there were no cars parked or people.

The piping was ‘protected’ with a PRV but it still came through and caused severe damage.

I now propagate that all such installations be protected by a PRV, and also by a water hammer arrester as a safety precaution. Some PRV valves have a built-in water hammer arrester.

The design and construction of a building water installation is ‘dictated’ by the three municipal water supply conditions and it is the responsibility of the owner to accept it ‘as is’, or to secure it by means of technical solutions and engineering design.

Water hammer can cause serious problems, damage, and is a safety threat. It must be addressed in the design.

It is essential to train facilities management services, plumbers, and their assistants, to slowly open and close water supply valves to prevent water hammer.

Other fixtures that cause water hammer are the solenoid valve that you find in a kitchen canopy and the one that you find in the water supply to an irrigation system, and also where there is a small pump that suddenly starts and stops.

It has also been found that water hammer is created by a certain water meter.

Water hammer can cause serious damage to water piping with spigot and socket plastic piping, even when the piping is more than one-meter deep underground.

I had a case where a small pump in a factory started and stopped suddenly and caused huge surges of water hammer in a 300mm-diameter pipe one-meter underground and after six months, the joints were worn out and the piping had to be replaced.

It is recommended that the flow velocity in a pipe in a building above ground should be around one to 1.5m/second to prevent noise and water hammer.

Please note that water hammer is not a hammer you can purchase at the hardware shop (just a little joke).

What is a water hammer arrester?

When a valve closes quickly and stops the flow, that momentum shakes and pounds pipes. Water hammer arresters cure this condition with a cushion of air that absorbs the momentum. Before you install arresters, determine which faucets or valves in your house cause the noise.

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