What causes low water pressure — and when is it serious?

Low water pressure doesn’t automatically mean you need new pipes. The pattern — one fixture or all, sudden or gradual, hot side or both — points at the cause, and most causes are far smaller than a repipe.

One fixture: look at the fixture

A single weak faucet or shower is almost always local — a clogged aerator screen, a scaled showerhead, or a half-closed angle stop under the sink. Unscrew the aerator and rinse it before calling anyone.

Whole house, sudden: valve or regulator

Pressure that dropped overnight points at the pressure regulator (the bell-shaped brass fitting where water enters the house) or a main valve that’s failed or been partially closed. Regulators are wear items — 10–15 years is a typical life — and a failed one can swing pressure low or dangerously high.

Whole house, gradual over years: pipe material

Slowly fading pressure, worst on hot, often with rusty morning water, is the signature of galvanized steel pipe corroding shut from the inside. Common in pre-1965 Sonoma County homes that haven’t been repiped. This is the one cause where a repipe conversation is honest — after a proper inspection confirms it.

Hot side only: the water heater

Good cold pressure but weak hot points at the water heater or its valves — sediment, a dip-tube failure, or a partially closed inlet. Much cheaper than anything involving walls.

The ten-minute test worth doing

A $15 gauge on a hose bib reads your static pressure in seconds. 40–80 PSI is the healthy range; below 40 confirms a supply problem, above 80 means your regulator needs attention before it shortens the life of everything downstream. We check pressure on nearly every service call because it explains so much.

Still not sure what you're looking at?

Call (707) 228-4595 and describe it — we'll tell you what it probably is and whether it needs a visit.

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