What causes low water pressure in the whole house?
Whole-house low pressure is almost always the pressure-reducing valve (PRV) at the main shutoff, a partially-closed main valve, a clogged whole-home filter, or mineral buildup inside old galvanized pipes. A single fixture with low pressure is usually an aerator or supply-line issue.
Whole-house low pressure is almost always the pressure-reducing valve (PRV) at the main shutoff, a partially-closed main valve, a clogged whole-home filter, or mineral buildup inside old galvanized pipes. A single fixture with low pressure is usually an aerator or supply-line issue.
If every fixture in the house is weak, the problem is upstream of the fixtures. The most common culprit is a failing pressure-reducing valve (PRV) at the main — these typically last 10-15 years and then drift low.
Second most common: a whole-home carbon or sediment filter that hasn't been changed and is now acting like a clog. Third: the main shutoff valve has been partially closed and forgotten about. Fourth: old galvanized pipes narrowing from mineral buildup (more common in homes built before the mid-1980s).
If it's only one fixture — a sink, one shower — the fix is usually the aerator, cartridge, or a kinked flex line at that fixture, not a whole-house problem.
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Last reviewed April 1, 2026.