Test your water pressure and flow

How we work it out

Pressure. Screw a pressure gauge onto the hose bib nearest the water meter. Turn off every tap in the house first. That reading is your static pressure. It drops when the neighbours water, so test on a summer morning and use the lowest reading.

Flow. Open the same hose bib all the way and time how long it takes to fill a bucket. Rain Bird gives it as 300 ÷ seconds for a 5 gallon bucket, which is the same as:

gpm = gallons × 60 ÷ seconds

Design flow. Plan each zone on 75% of that, so the sprinklers still work when someone runs a tap. Rain Bird and the Irrigation Association also say not to use more than 75% of the meter's safe flow, so a 5/8 in meter (about 20 gpm) caps you near 15 gpm, however fast the bucket fills.

design flow = smaller of (bucket gpm, meter gpm) × 0.75

Hills. Water loses 1 psi for every 2.31 ft it climbs, so a lawn 10 ft above the hose bib has about 4 psi less.

What it runs. Spray heads work best at 30 psi at the head, rotary nozzles at 45, and rotors at 40 to 50. You lose 10 to 15 psi in the meter, backflow and pipe, so we want about 35 psi static for sprays and 40 to 45 for rotors and rotary nozzles. Over 80 psi, the house needs a pressure-reducing valve.