What is the difference between water pressure and flow rate?

Water pressure is the force available to move water, while flow rate is the volume delivered over time. A tap can have reasonable static pressure but poor flow through a restriction, so the two measurements answer different questions.

Pressure is commonly expressed in bar or as metres of head. WaterSafe explains that 10 metres of head is approximately one bar. Flow is normally expressed in litres per minute and can be estimated by timing how long an outlet takes to fill a container of known volume.

Partly closing a stop tap adds a restriction and reduces flow when water is running; it is not proper pressure control. Where pressure genuinely needs controlling, a plumber can assess whether a pressure-reducing valve is appropriate and set it for the installation and appliances.

Compare like with like. Measure at the same outlet, with other outlets and appliances off, and repeat at different times if the problem is intermittent. If the incoming supply appears below the expected service level, take the observations to the water supplier rather than buying a pump first.

The distinction explains why two complaints can feel similar. A blocked aerator may give poor flow from one tap even though pressure elsewhere is normal. Conversely, a pressure gauge can show a reasonable reading while a small or restricted pipe cannot deliver enough water when several outlets open together. Pumps and pressure controls also have rules and compatibility limits. Before changing equipment, identify the system, collect both pressure and flow information where appropriate, and check the appliance maker's requirements.

Sources

• What should my water pressure be? — WaterSafe, accessed 14 November 2026.
• What causes water pipes banging? — WaterSafe, accessed 14 November 2026.

On Leatmere

See water pressure testing, pressure-reducing valves and the glossary entries for flow rate and pressure-reducing valve.