What is typical UK mains water pressure?

UK mains water pressure is usually between 1 and 4 bar, with 3 bar being a common average. Your water company can confirm your supply pressure, or use a simple gauge on an outside tap.

Does pipe length affect water pressure?

Yes. Friction losses increase with pipe length. A 50m run of 15mm pipe loses significantly more pressure than a 10m run. Larger pipe diameters reduce friction loss.

Can I run irrigation from a water butt?

Yes, but gravity-fed water butts only provide about 0.1-0.3 bar. You need low-pressure drippers or a small pump. Standard sprinklers will not work from a water butt.

What pipe size should I use?

15mm is fine for short runs with few outlets. For longer runs or more outlets, step up to 22mm or 25mm to maintain adequate pressure and flow.

How does height difference affect pressure?

Every 1 metre of height difference adds or removes about 0.1 bar. Water flowing uphill loses pressure; downhill gains it. This matters especially for water butt gravity systems.

GardenCalcs

Water Pressure Calculator — Garden Irrigation Pressure & Flow

Calculate water pressure and flow rate for garden irrigation systems.

Water SourceWater source

Pipe DiameterPipe Diameter

Pipe Run Length

Pipe run length

Number of Outlets

Number of outlets

Height Difference

Positive = uphill, negative = downhill

How We Calculate This

Pressure at the end of a pipe run is calculated by subtracting losses from the source pressure.

Losses: Height loss = height × 0.098 bar/m. Friction loss = length × friction factor × (reference diameter / actual diameter). Fitting loss = outlets × 0.05 bar.

Flow rate is estimated from the remaining pressure and pipe cross-section area. Maximum sprinkler count is based on a typical sprinkler flow rate of 6 L/min.

Frequently Asked Questions

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Last updated: March 2026

All calculations are estimates based on standard gardening guidelines. Results may vary with soil conditions, climate, and plant varieties.