The pressure in the house is good but when the sprinkler system turns on outside the pressure drops in the house. I don’t believe this has always been the case or maybe I didn’t notice but it seems to be a new thing.

  • check your water pressure regulator outside, during both events
    – Traveler
    Commented Aug 25, 2023 at 5:07
  • Do you mean pressure, or flow-rate?
    – Tetsujin
    Commented Aug 25, 2023 at 6:39
  • It is normal for pressure and flow to drop when more than one outlet is being used, and especially when one of them is a sprinkler system. But perhaps you have a new problem where the effect is much worse than before. This could be caused by a new blockage or constriction in the pipe that feeds both inside and outside, or by a damaged pipe or head in the sprinkler system. Do all the sprinkler heads work similarly well to one another and to the way they worked before you noticed this problem? Does one zone spray poolrly? Do all zones spray worse than before you noticed the problem?
    – jay613
    Commented Aug 25, 2023 at 12:28

1 Answer 1


The logical and common reason for this is a leak in the sprinkler system.

Of course this is assuming that the sprinkler is fed by the same supply line as the home.

Depending on the type of layout for your irrigation, you may have a loop around the house with each zone being fed by inground zone valves. Or you may have a single supply to a manifold of valves. This is usually located close to where the house water supply comes into the home. Each zone is branched off of the manifold. It will take a little bit of investigating to find the area where the issue is.

Often a root from a tree or a large bush cracks a pipe or causes a fitting to be disconnected. Then when the sprinkler is active you lose considerable pressure from the damaged area.

Take a walk around the yard and look for a spot where the ground is extra damp or muddy. That will give you an indication that the leak may be in that area.

Check your house pressure when each zone is turned on. If the drop occurs only with one particular zone on, then the leak is in the piping for that zone. If the pressure drop is experienced with every zone, the leak will most likely be in the main line.

One of the common places for a leak is where the irrigation supply ties into the home supply line. Often it is deep enough that the evidence of the leak is not easily visible.

I have found leaks in the ground with a mechanics stethoscope. Push it in the ground and if there is a leak around you will hear a roaring or hissing sound. Good Luck.

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