Dry patches, uneven coverage, or a fine mist that blows away

What has gone wrong

The system runs, the heads come up, and the lawn still has brown patches. Three different faults look like this.

• Dry patches between heads. Worn nozzles throw shorter than they used to, so the overlap that used to cover the gap no longer reaches. Sprinklers are meant to be spaced so each head's spray reaches the next head — lose a metre of throw and the middle goes dry first.
• An arc watering the fence, the path or the neighbour. The nozzle has been knocked round, or it is the wrong arc for where the head ended up.
• A fine mist that drifts away before it lands. That is pressure too high for the nozzle fitted. You are paying for water that never reaches the lawn, and on a windy day most of it leaves the property.

If every head is weak rather than uneven, this is the wrong page — that is low pressure everywhere.

Why this happens in Perth

The watering roster is what makes this expensive rather than cosmetic. Perth allows sprinklers two days a week, and inspectors are out seven days with a $100 fine. So the usual response to a dry patch — run it more often — is not available to you. Two days a week has to be enough, which means the water has to actually land where the grass is.

Sandy soil makes it show up faster. Perth sand holds very little water, so a spot getting 80% of what its neighbour gets does not look 20% worse, it browns off while the rest stays green.

Misting is the one that costs the most and gets noticed the least. Bore systems in particular often run at more pressure than a spray nozzle wants, and fine droplets in a Perth easterly are simply gone.

Is this a DIY job?

Yes. Everything below is 24V AC or purely mechanical, which is the part of a reticulation system a homeowner can safely work on.

The catch-cup test, and three free fixes

Measure it before you buy anything. Put six or eight identical containers — tuna tins, takeaway containers, anything with straight sides — around the affected area, including in the dry patch and in a part that is doing fine. Run the station for fifteen minutes. Compare the depths.

That turns "I think it is dry over there" into a number, and it tells you whether the problem is coverage or something else entirely. If the dry patch tin has half what the good patch has, it is coverage. If they are the same, your dry patch is not a reticulation fault — look at soil, shade, or a tree taking the water.

Free fix one: clean the nozzles. Unscrew the nozzle from the raised head, pull out the small filter basket underneath it, and rinse both. On bore water these silt up with fine sand and iron, and a half-blocked nozzle throws short and patchy. This costs nothing and it is the first thing to do.

Free fix two: reset the arcs. With the station running, turn each nozzle so it covers lawn and not fence, path or driveway. Most adjustable nozzles turn by hand or with a small screwdriver in the slot on top. Watering the footpath is free water you are already paying for.

Free fix three: turn the misting down. Nearly every solenoid valve has a flow control — a screw or a small handwheel on top of the bonnet, above the solenoid. Turning it clockwise throttles that station. With the station running, wind it down slowly until the mist turns into visible droplets and stops drifting. You will often gain throw rather than lose it, because the water is no longer being atomised.

Do it one station at a time and give each a moment to settle. If winding it down kills the throw entirely, you have gone too far — back it off.

Replacing nozzles

If the catch-cup test says coverage and cleaning did not fix it, the nozzles are worn. They are the cheapest part of the whole system and the one that most affects whether the lawn survives on two days a week.

1. Run the station so the heads are up. Some people prefer to pull each head up by hand with the station off and hold it — either works.
2. Unscrew the old nozzle and lift out the filter basket. Keep the basket; it goes back in.
3. Fit the replacement with the same arc: quarter for a corner, half for an edge, full for the middle. A half nozzle in a corner position waters the fence.
4. Hand-tighten only. Plastic threads.
5. Run the station and watch the spray reach the next head. If it does not, that is the spacing, not the nozzle — and spacing is a design problem, not a maintenance one.

Do the whole station. Every nozzle on it is the same age and has done the same hours. Replacing the two obviously bad ones leaves you with six that are slightly bad, and the coverage still will not be even.

If misting will not go away

If the flow control is wound most of the way down and the spray is still misting, the system pressure is genuinely too high for those nozzles. The proper answer is pressure-regulating heads, which hold a fixed outlet pressure regardless of what arrives. That is a head replacement rather than a nozzle swap — see replacing a pop-up head, which is the same job.

What it costs

The catch-cup test, cleaning the nozzles, resetting the arcs, and turning the flow control down: nothing at all. Do all four before you spend a cent, because between them they fix a good proportion of coverage complaints.

Nozzles: the cheapest part on the system, sold individually and in packs. We have not verified current Perth pricing, so ask a supplier rather than trusting a figure from elsewhere.

Pressure-regulating heads: dearer than plain ones, and unverified. Worth it only where misting persists after the flow control is wound down.

If you pay somebody: unverified. A coverage job is worth quoting per station rather than per head — ask for it that way.

Common questions

Why does my lawn have dry patches between the sprinklers?

Worn or blocked nozzles throwing shorter than they used to. Sprinklers are spaced so each head’s spray reaches the next one, so losing throw makes the middle go dry first.

How do I stop my sprinklers misting?

Wind down the flow control on top of the valve bonnet with the station running, until the mist turns into visible droplets. Misting is pressure too high for the nozzle fitted.

How can I measure sprinkler coverage myself?

Put identical straight-sided containers around the area, including in the dry patch, run the station for fifteen minutes and compare the depths. Equal depths mean the dry patch is not a coverage fault.