How much water does my lawn need?
Quick answer
It depends on your climate, soil, grass and the season, so measure rather than guess. As one official example, Water Corporation says gardens and lawns in Perth and the South West need 10 mm of water twice a week in summer, and far less in cooler months. Water deeply and less often, follow your local water rules, and use a catch-cup test to see what your sprinklers deliver.
Why this happens
There isn’t one number that suits every Australian lawn. How much water a lawn needs depends on the weather (hot, windy days lose far more water than mild ones), the soil (sand drains quickly, clay holds on), the grass type and whether it’s in sun or shade.
What we can give you is a reliable way to work it out, and one official benchmark. Water Corporation advises that in Perth and the South West, gardens and lawns need 10 mm of water, twice a week in summer, and much less in the cooler months. Watering more than that doesn’t help, and overwatering can leach nutrients out of the soil. Your own water authority may publish guidance for your area; check it, along with the current watering rules.
Think in millimetres, not minutes
Rain and irrigation are both measured in millimetres of water depth. Your sprinklers don’t put out the same amount per minute as your neighbour’s, so “20 minutes” means nothing until you know your system’s rate. A catch-cup test gives you that: set out straight-sided containers, run the zone for a set time, and measure the depth. The Sprinkler Run-Time Calculator turns the result into minutes.
Deep and less often
Applying the full amount in one session encourages roots to grow down to where the water is, which helps the lawn ride out hot spells. Little-and-often watering keeps the surface damp, roots shallow and the lawn dependent on you.
Signs you’re getting it wrong
Underwatering: grass that stays folded or bluish-grey, footprints that don’t spring back, and dry soil a few centimetres down. Overwatering: soggy soil days later, more weeds and disease, and run-off down the driveway.
It depends on your grass and climate
| If you have… | What changes |
|---|---|
| Perth and the South West | Water Corporation's guidance is 10 mm twice a week in summer, less in the cooler months, on your rostered days. |
| Sandy soils | Sand holds less water, so water may need to be applied more often in smaller amounts, and water-repellent sand needs a wetting agent first. |
| Clay soils | Clay holds more water but takes it in slowly. Apply it in shorter cycles so it soaks in rather than running off. |
| Shaded lawns | Lawns in shade lose less water, but tree roots can take a lot of it. |
Rows that match the grass and climate zone you've set are highlighted. Set your climate zone
What you can do
Check your local water rulesCheck first
Your water authority sets which days and times you can water, and these change. Check before setting a schedule.
Measure what your sprinklers deliverCheck first
Do a catch-cup test. It tells you how many millimetres each zone puts out per minute and how evenly.
Water deeply and less often
Apply the amount you're aiming for in one session (or two short cycles on heavy soils), rather than a little every day.
Adjust for the season
Reduce watering in the cooler months and after rain. Water Corporation notes gardens need far less in cooler months.
Fix dry patches separately
Areas that stay dry despite watering usually need a wetting agent or better sprinkler coverage, not more water everywhere.
What not to do
- Watering a little every day, which keeps roots shallow.
- Running sprinklers on a fixed timer all year without adjusting for season or rain.
- Watering harder to fix one dry patch, and overwatering the rest of the lawn.
How much do I need?
Place straight-sided containers around the zone, run it for a set time, then measure the depth of water in each with a ruler. How to do a catch-cup test
Run time for this zone
Enter at least two cup readings, the test time and the water you want to apply.
Log it
Keep a record of what you applied, when, and at what rate. Your Lawn Journal works on this device without an account, and reminds you when the next step is due.
What's next
Related grass types, weeds, pests and diseases
Lawn problems
Related questions
Related guides
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Sources
- How much water does my garden need?, Water Corporation (Western Australia)10 mm twice a week in summer for Perth and the South West; less in cooler months; overwatering can leach nutrients. Accessed 4 October 2026.
- How long should I run my sprinklers for?, Water Corporation (Western Australia)Catch-cup test. Accessed 4 October 2026.