Weak pressure at one faucet is usually local — a clogged aerator, a single bad valve. Weak pressure everywhere in the house is a different problem, and the fix depends on correctly identifying which of a few likely causes you're actually dealing with.
📅 Updated: August 2026🏠 Topic: Plumbing⏱ 6 min read
Quick Answer
Whole-house low pressure almost always comes from one of four sources: a failing pressure-reducing valve (PRV), corroded galvanized supply pipes narrowing from the inside, a clogged whole-house sediment filter, or a partially closed main shut-off valve. Test the pressure at an outdoor spigot with a gauge before replacing anything — the reading tells you which of these you're dealing with, and guessing wrong means paying for a fix that doesn't address the actual cause.
What's actually causing it
Low pressure at every fixture — not just one — narrows the list considerably. The cause sits somewhere between the street connection and the point where your plumbing branches out to individual fixtures, which is why the symptom shows up everywhere at once instead of in one room.
The Four Most Likely Causes
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Failing pressure-reducing valve (PRV) — Most homes on municipal water have a PRV where the main line enters the house, set to keep incoming pressure in a safe range. PRVs fail gradually over 8–12 years, and a failing valve typically drifts toward under-delivering rather than over-delivering. If pressure has dropped slowly over months rather than suddenly, this is the first thing to check.
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Corroded galvanized pipe — In homes with original galvanized steel supply lines, internal corrosion narrows the pipe diameter over decades, restricting flow throughout the system. This is a progressive problem with no single fix short of a partial or full re-pipe. See our guide on types of pipes used in home plumbing to confirm what's actually running through your walls before assuming this is the cause.
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Clogged whole-house sediment filter — If your home has a whole-house filter installed after the meter, sediment buildup restricts flow to the entire house even though nothing else has changed. This is the easiest cause to rule out — check the filter housing before assuming a bigger problem.
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Partially closed main shut-off valve — Common after any plumbing work near the meter. A valve that isn't fully open restricts flow to the whole house and is often overlooked because it's assumed to be "done" once turned. Worth ruling out first — it costs nothing to check.
Diagnose it before you fix anything
Guessing at the cause and replacing parts one at a time is expensive and slow. A five-minute test narrows it down first.
Test pressure at an outdoor spigot. Thread a water pressure gauge onto any hose bib and open it fully. Normal residential pressure runs 40–80 PSI; most homes are comfortable in the 50–70 PSI range. A reading below 40 PSI confirms the problem is real and system-wide, not just a perception issue with one fixture.
Confirm the main valve is fully open. Located where the main line enters the house, near the meter. A gate valve should be turned counterclockwise as far as it goes; a ball valve handle should sit parallel to the pipe, not at an angle. This takes thirty seconds and rules out the cheapest possible cause first.
Check the PRV setting and condition. If your home has one, it's typically a bell-shaped valve on the main line with an adjustment screw on top. A reading well below the PRV's set point suggests the valve itself is failing internally rather than just needing an adjustment.
When It's Not Something You Can Diagnose Yourself
If pressure tests low at the spigot, the main valve is fully open, and there's no whole-house filter to check, the most likely remaining cause is pipe corrosion or a municipal-side issue — neither of which has a homeowner-level fix. A licensed plumber can pressure-test individual sections to isolate exactly where the restriction is before recommending a repipe or other work.
What actually fixes each cause
Once you know the cause, the fix is usually straightforward. A failing PRV is replaced, not repaired — they're not designed to be serviced internally, and a $40–$80 part is cheaper than the water damage a fully-failed valve can eventually cause. A clogged sediment filter just needs its cartridge replaced, often resolving the problem within minutes. A partially closed valve is a non-issue once corrected.
Corroded galvanized pipe is the one cause without a quick fix — the narrowing is internal and progressive, and cleaning or lining old galvanized pipe is rarely cost-effective compared to replacement. If pressure has been declining for years rather than months, and your home was built before 1960, this is the most likely explanation and worth getting a professional opinion on sooner rather than later.
If pressure tests low even though the incoming municipal supply is fine — confirmed by a neighbor with normal pressure on the same line, or by the utility company directly — a whole-house booster pump restores usable pressure without waiting on infrastructure repairs outside your control.
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Normal residential water pressure runs 40–80 PSI, with most homes comfortable in the 50–70 PSI range. Below 40 PSI, fixtures and appliances start to underperform noticeably — showers feel weak, washing machines take longer to fill. Above 80 PSI creates its own risks, including premature wear on fittings and water heaters, which is exactly what a PRV is designed to prevent.
Why did my water pressure drop suddenly instead of gradually?
A sudden drop points to something mechanical rather than gradual wear — a partially closed valve, a sudden PRV failure, a clogged filter reaching capacity all at once, or a municipal-side issue affecting your street. Gradual decline over months or years is more consistent with PRV wear or pipe corrosion. The timeline itself is diagnostic information worth noting before you call anyone.
Is low water pressure a sign I need to repipe my house?
Not necessarily. A repipe is only the answer when the cause is confirmed pipe corrosion — typically in homes with original galvanized steel supply lines that are decades old. A failing PRV, a clogged filter, or a partially closed valve all produce the same symptom but have far simpler and cheaper fixes. Testing and ruling out the easy causes first avoids an unnecessary repipe recommendation.
Can a water softener or filter cause low pressure throughout the house?
Yes. Any whole-house treatment device — softener, sediment filter, carbon filter — sits in the main line and restricts flow if its media or cartridge is clogged. This is one of the more overlooked causes because homeowners forget the device exists until it starts affecting pressure. Checking or replacing the filter cartridge is a quick, low-cost step worth doing before assuming a bigger problem.
Should I call the water company before a plumber?
If a neighbor on the same street reports normal pressure, the issue is inside your home and a plumber is the right call. If pressure is low or inconsistent across the neighborhood, the municipal supply or a street-level issue may be responsible, and the water utility can confirm whether there's a known issue in your area before you spend money diagnosing something outside your control.