How much water does a garden need?
Most lawns need about 1 in (25 mm) of water a week, from rain and watering combined. In hot, dry spells that can rise to 1.5 in (38 mm). Established shrubs need less. Deep watering once or twice a week grows deeper roots than a little every day.
Cool season lawn
1 in (25 mm) a week
Warm season lawn
0.75 in (20 mm) a week
Vegetable garden
1 in (25 mm) a week
Shrub and flower beds
0.5 in (13 mm) a week
Planning the rest of the job? Use the Lawn area calculator and the Pond volume calculator too.
How does the calculation work?
Gallons = area (ft²) × inches of water × 0.623 ÷ efficiency
A 2,000 ft² lawn needing 1 in a week takes 1,246 gallons. Sprinklers lose about a quarter to wind and evaporation, so plan on about 1,660 gallons.
In metric it is simpler: 1 mm of water on 1 m² is 1 litre. A 185 m² lawn needing 25 mm takes 4,625 litres before losses.