Puddles at the Lowest Sprinkler Head: Low-Head Drainage Explained

If you notice a puddle or soggy area around one sprinkler head, usually at the lowest point of the yard, and water keeps trickling out of that head for a while after the zone shuts off, you are probably seeing low-head drainage. It is common, especially in yards with even a slight slope. This article explains what it is, how to tell it apart from a stuck valve, and how it is fixed.

What Low-Head Drainage Is

When a zone shuts off, the pipe between the valve and the heads is still full of water. Gravity pulls that water to the lowest point in the zone. If the lowest head has no way to hold the water back, it drains out through that head until the pipe is empty.

Each time the zone runs, the pipe fills again and drains again. The result is a patch around the low head that gets far more water than the rest of the lawn. Over time you may see:

• A soggy or muddy spot that never quite dries
• Moss, algae or fungus around the head
• Grass that is thin, yellow or thatchy from too much water
• A sunken area where soil has washed out
• Water running across a sidewalk or into the gutter

Low-Head Drainage vs. a Stuck Valve

These two look similar at first, but the difference is easy to see:

• Low-head drainage trickles out slowly and stops on its own once the pipe is empty, usually within several minutes, depending on the slope and pipe length.
• A stuck or leaking valve keeps water flowing. It may be a steady trickle that never stops or full flow from every head.

If water continues for a long time, or keeps coming back between cycles, look at the valve. Our guide on a zone that will not turn off explains how to check it. You can also see our article on sprinkler valve repair.

Why It Is Common in Fort Worth Yards

Many Fort Worth lots slope from the house toward the street, or have gentle rolls in the back yard. Even a small drop can drain a surprising amount of water to the low head. Clay soils absorb water slowly, so the drained water tends to puddle rather than soak in. Our article on clay soil and sprinkler systems explains how clay affects watering.

How It Is Fixed

Check valves in the head

Many spray heads and rotors are available with a built-in check valve, a small spring-loaded seal that holds water in the pipe until pressure reaches a certain level. When the zone shuts off, the check valve closes and the water stays in the pipe instead of draining out.

For some heads, a check valve can be added as a separate part that fits in the riser or under the nozzle. For others, replacing the head with a check-valve model is simpler.

Which heads need them

Usually only the lowest few heads on a zone need check valves. On steeper slopes, more heads may need them. Adding check valves to the heads at the bottom of the slope first, then checking again, is a sensible approach.

Fixing the soil and turf

Once the drainage stops, let the soggy area dry out. Fill any sunken spots with soil, and reseed or re-sod if needed. If the area has poor drainage even without the extra water, grading or drainage work may help. Our drainage service handles that side of the problem.

Other Causes of Puddles Near Heads

Not every puddle is low-head drainage. Other possibilities include:

• A cracked fitting under the head, which leaks while the zone runs
• A broken head that gushes
• A lateral leak nearby
• Runoff from a slope where water is applied faster than it soaks in

Our article on signs of a hidden sprinkler leak can help you rule these out. For runoff, see our guide to stopping runoff on clay and slopes.

Does It Waste Water?

Low-head drainage wastes the water held in the pipe each time the zone runs. On a zone that runs twice a week, that adds up over a season. It also means the rest of the zone gets a little less water at startup, since the pipe has to refill before heads reach full pressure. And if the drained water runs across a sidewalk or into the street, it counts as runoff under Fort Worth’s watering rules.

Checking After the Fix

After check valves are installed, run the zone and watch the low heads when it shuts off. Water should stop within a second or two. Check again a week later to make sure the area is drying out between cycles.

Heads on Retaining Walls and Terraces

Yards with retaining walls or terraces often have low-head drainage on the lower level, since the pipe running down from the upper level holds a lot of water. The heads at the base of the wall can drain for several minutes, soaking the soil against the wall. Water held behind a retaining wall is not good for the wall. Check valves on the lower heads, and sometimes a separate zone for the lower level, help keep the soil at the base of the wall from staying saturated.

When to Call a Technician

If you are not sure whether you have low-head drainage or a valve leak, or you need check valves added to several heads, our sprinkler repair team can diagnose and fix it.