Groundwork

Water pressure

Water pressure describes the flow strength of water through a pipe. The more water being pushed through a pipe the more pressure there will be.

Water pressure is measured and expressed in kilopascals (kPa) and metres head (m head).

Many people prefer high water pressure to low water pressure. Valves and other devices can be installed to reduce water pressure but there is little that can be done to improve water pressure that is very low.

Open icon Measuring pressure

The term 'head' refers to the pressure in plumbing pipe systems. It is measured in metres. Head loss is the loss of water pressure as it moves through a pipe system due to friction between the fluid and the walls of the pipe.

You need to know the water pressure available to you when designing a hot or cold water system for a property. The water authority can provide you with the maximum and minimum pressure for the water main. You also need to allow for the head loss.

Worked example – Calculating water pressure

To calculate water pressure use the formula.

Graphic of equation to calculate water pressure. The equation is P equals h multiplied by 9.81 kPa. In the equation P equals water pressure (kPa), h equals head (height above outlet in metres), 9.81 kPa equals pressure exerted by 1 m head of water under the force of gravity. A worked example is shown.