Low Water Pressure: Causes and Fixes

The fastest triage question before touching anything else: does only one faucet or showerhead have low pressure, or is every fixture in the house affected? These are completely different problems with completely different causes.

Single-fixture low pressure (everything else tests normal):

• Clogged aerator — the most common cause by a wide margin. The aerator is the threaded screen-and-flow-restrictor assembly at the tip of the faucet spout. Mineral scale, debris, and biofilm accumulate inside it over time. Fix: unscrew the aerator counterclockwise (by hand or with pliers wrapped in a rag), soak it in white vinegar for 30 minutes, rinse under running water, reinstall. Restores full flow in approximately 90% of single-fixture low-pressure calls. Replacement aerators run $3–5 at any hardware store if the screen is corroded beyond cleaning.
• Kinked or crimped flex supply line — the corrugated stainless braided flex connector running from the angle-stop shutoff valve to the faucet body can kink if the cabinet below the sink was reorganized, a drain pipe shifted, or someone crawled under the sink for repairs. Look under the sink: the connector should run in a gentle curve with no sharp bends. A kinked connector restricts flow without leaking — it's easy to miss on a visual check unless you look closely at the full length.
• Failing angle-stop valve — the shutoff valve under the fixture (the oval-handled knob behind the supply connector) may be partially closed or have a deteriorated internal packing that restricts flow even when nominally open. Try closing and fully reopening it. If the handle feels stiff or won't turn a full quarter-turn, the valve should be replaced.
• Clogged showerhead — mineral scale accumulates inside the showerhead body and especially inside the integral flow restrictor (a small plastic disc with a pinhole at the inlet). Fix: remove the showerhead, submerge it in white vinegar overnight, flush with water before reinstalling. If the showerhead is more than 8–10 years old in a hard-water market, replacement ($20–60) is faster than cleaning.

Whole-house low pressure means the restriction is upstream of every fixture — the pressure-reducing valve (PRV), the main shutoff, a supply-line restriction, a corroded galvanized system, or low municipal street pressure. Diagnose with a pressure gauge ($15–40) threaded onto the outdoor hose bib closest to the main shutoff. A reading below 40 PSI confirms a whole-house problem and tells you where to look next.

Before diagnosing a cause, get a number. Buy a water pressure gauge ($15–40 at any hardware store) with a standard hose-bibb fitting. Thread it onto an outdoor hose bib close to the main shutoff — not at the far end of the house. Open the bib fully, read the gauge.

• Below 40 PSI — definitively low. Most plumbing fixtures and appliances are rated for minimum 40 PSI per IPC Section 604.8.
• 40–80 PSI — normal operating range. If pressure feels low at specific fixtures, the problem is downstream of the main (a clogged aerator, a failing fixture shut-off, a kinked flex supply line).
• Above 80 PSI — too high, not low. High pressure accelerates valve wear and causes water hammer. A PRV is required.

Also test pressure at the street meter (if accessible). If street pressure is already below 45 PSI, the fix is outside your home — contact your water utility. Utilities are required by EPA Safe Drinking Water Act regulations to maintain minimum service pressure at the meter.

If your home has a pressure-reducing valve — a bronze bell-shaped fitting on the supply line where it enters the house — it's the most common culprit in sudden pressure drops. PRVs are set at the factory for 50–60 PSI and have a lifespan of 7–15 years. When they fail they can stick closed (very low pressure), fail to reduce high street pressure (high pressure → hammer noise → appliance damage), or flutter erratically (fluctuating pressure).

Testing a PRV: measure pressure at the hose bib before and after the PRV with the valve in line. If street pressure at the meter reads 90 PSI and downstream reads 28 PSI, the PRV is restricting more than it should. The fix is a PRV replacement ($200–450 parts + labor). PRV replacement requires the main shutoff to be closed and is a licensed-plumber job in most jurisdictions because the shutoff is often near or at the meter.

PRVs also have a brass adjustment screw under a locknut on the top of the bell. If your pressure dropped recently and the PRV is under 7 years old, a previous owner or plumber may have turned it down. Loosening the locknut and turning the screw clockwise raises pressure — but only up to the PRV's set maximum (typically 75 PSI). If the adjustment range won't restore normal pressure, replace the PRV.

Homes built before 1970 often have galvanized steel supply pipes. Over decades, iron oxide and mineral scale build up on the inside of the pipe, progressively narrowing the interior diameter. A ¾" galvanized pipe with 50 years of scale can have an effective bore of 3/8" or less. This manifests as low pressure that gets worse year over year, often with rusty or discolored water.

The diagnostic test: disconnect a flex supply line at a shut-off valve under a sink, place the line in a bucket, and briefly open the valve. If flow is sluggish, the restriction is upstream. Walk the supply chain back — if flow is normal at the main shutoff but sluggish two branches down, the scale is localized to those branches.

Partial solutions (descaling, hydro-jetting supply lines) can help temporarily but won't fully restore a badly corroded galvanized system. The permanent fix is a whole-home repipe to PEX or copper per IPC Chapter 6 — supply pipe materials, typically $4,500–$15,000 depending on house size and market.

Copper pipes develop pinhole leaks rather than buildup, but hard-water scale on aerators and inside copper tees at fixture branches can reduce flow to individual fixtures. USGS water hardness data shows water above 10.5 GPG accelerates copper corrosion and scale deposition.

The most embarrassing cause of low pressure — and the most commonly missed. There are up to six shutoff points between the water main and any given fixture:

1. The utility's curb stop (at the street)
2. Your main house shutoff (typically where the main enters the foundation)
3. The PRV bypass (if any)
4. A zone shutoff (if you have a multi-zone supply)
5. The branch shutoff (often in a crawl space or basement ceiling)
6. The angle-stop shut-off under the fixture itself

Any of these, if not fully open, restricts flow. Gate valves (the older wheel-handle type) are notorious for breaking off internally — the handle turns but the gate stays partially down. If your main shutoff is a gate valve and it was recently exercised (after a repair, after a vacation), verify it's truly full-open: remove the handle, measure the stem position, or replace it with a ball valve. Ball valves are reliably either fully open (90°, lever parallel to pipe) or fully closed (90°, lever perpendicular). No ambiguity.

A supply-line leak downstream of the meter "bleeds" pressure before it reaches your fixtures. The tell-tale sign: your meter's low-flow indicator (a small triangle or dial on the face of the meter) keeps spinning when all fixtures are fully closed. If it moves at all, you have an active leak.

Turn off every fixture and appliance in the house. Go outside and watch the meter for 10 minutes. Any movement = leak somewhere. The leak is most likely in the first 6 feet of supply line inside the foundation (frost-cycle expansion/contraction stress point), under a slab (if you have radiant heat or in-slab supply runs), or at a corroded galvanized fitting in a crawl space.

A plumber can pressurize the line with nitrogen and use an electronic leak-detection sensor to locate leaks through concrete or soil without destructive access — important when the leak could be anywhere along a 50-foot run. Cost: $250–450 for detection; repair depends on location and method.

If street pressure is low at the meter (below 45 PSI) and you've confirmed it by checking with the utility, your options are:

• File a pressure complaint with the utility. Utilities must maintain minimum pressure at the meter under SDWA regulations. Document your gauge reading, date, and time. Chronic low pressure can trigger a main upgrade at the utility's expense.
• Install a water pressure booster pump. A residential booster adds $800–1,800 installed and can bring 35 PSI street pressure up to 65+ PSI inside the home. Requires a licensed plumber; must include a pressure relief valve per IPC Section 604.8.
• Add a pressure tank. Often paired with a booster; the tank maintains a pressurized reserve so the pump doesn't cycle on every demand spike (extends pump life 3-5×).

Cost ranges per BuildZoom 2024 plumbing repair cost data with labor indexed to BLS CPI plumbing labor index. DIY costs assume parts only; plumber costs include one service visit plus parts.

• Aerator cleaning: $0 (DIY, vinegar soak). Aerator replacement: $3–5 parts.
• Showerhead cleaning: $0 (DIY, vinegar soak overnight). Showerhead replacement: $20–60 parts.
• Angle-stop valve replacement: $75–150 per valve (plumber, parts + labor).
• PRV adjustment: $75–150 (plumber visit; requires pressure gauge verification before and after).
• PRV replacement: $200–450 parts + labor. Higher end for larger-diameter mains or units requiring permit in your jurisdiction.
• Supply-line leak detection: $250–450 (electronic detection; non-destructive, through slab or soil).
• Supply-line leak repair (accessible pipe): $250–600. Add $500–1,500 if the line is under a slab and requires jackhammering for access.
• Whole-home galvanized repipe to PEX: $4,500–15,000 depending on house size, story count, and local labor market.
• Water pressure booster pump installed: $800–1,800 including the pump, pressure tank, and licensed install.

What requires a licensed plumber: everything except aerator and showerhead cleaning/replacement. PRV replacement and booster pump installation require a permit in most jurisdictions — confirm with your local building department before work starts. Unpermitted PRV work can void the manufacturer's warranty and create insurance complications if a pressure-related failure damages appliances downstream.