- Small leaks rarely change pressure noticeably; breaks usually do.
- Whole-house low pressure plus a moving meter is the classic combination.
- Old galvanized pipe can cause low pressure with no leak at all.
Think of your service line as a single road into town. A pothole slows a few cars; a washed-out bridge stops traffic. Water behaves similarly: a pinhole leak lets a trickle escape and pressure at the tap barely changes, while a split or separated joint gives water an easy exit before it ever reaches your fixtures.
Why a break lowers pressure
Water pressure at your tap depends on supply pressure minus the losses along the way. A large opening in the line creates a path of low resistance, so more of the flow heads out through the break. The effect is most obvious when you're using water: the shower weakens when someone runs the kitchen tap, or pressure sags and then partly recovers.
When pressure loss points to a buried break
- Pressure dropped suddenly across the whole house.
- Your neighbors are fine, so it isn't the City main.
- The meter keeps moving with the house and irrigation shut off.
- There's wet ground, pooling or a sinking spot between the meter and the house.
All four together is about as clear as a diagnosis gets without a plumber.
Low pressure without a leak
Not every pressure problem is a break. Two other causes often get confused with it:
- Corroded galvanized pipe: rust narrows the pipe from the inside over years. Pressure fades gradually, especially when two fixtures run at once, and the meter test shows no leak.
- A failing pressure regulator or partly closed valve: check your building shut-off, the customer valve in the meter box and any pressure-reducing valve near the main entry.
Our guide on sudden water pressure drops goes through each possibility.
What to do
- Check with neighbors to rule out a City issue.
- Run the meter test.
- If the meter moves and you can see water, shut off your customer valve (house side of the meter) or building shut-off between uses to limit loss.
- Call for a repair.
A buried break is handled through underground water line repair; if the failure is near the house entry or shut-off valve, main water line repair covers that scenario. For the full local picture, see our San Luis Obispo water line repair overview.