What Causes Low Water Pressure in Your House?
Five common causes of low water pressure in residential homes, and what each one costs to fix. From quick aerator cleanings to galvanized pipe replacement in older Greater Boston homes.
Low water pressure is one of the most common calls we get in older Massachusetts homes. It's also one of the most misdiagnosed — most homeowners assume it's a 'house thing' that can't be fixed, when in fact most low-pressure issues have a specific, identifiable cause that's fixable. Here's the diagnostic process we run on every low-pressure call, and what each cause typically costs to fix.
Cause #1: Clogged faucet aerators
The cheapest possible cause. The little screen at the tip of your faucet (called an aerator) catches mineral buildup and sediment over time. After 5-10 years it can clog enough to cut flow noticeably. The fix is a 30-second unscrew, soak in vinegar overnight, rinse, and reinstall. If this fixes it on one specific faucet, you don't have a house pressure problem — you have a fixture problem. Common in Billerica and Woburn where the water is moderately hard.
Cause #2: Pressure regulator failure
If your home is on city water, there's usually a pressure-reducing valve (PRV) where the main water line enters the house. These last 8-15 years and then start failing — either letting too much pressure through (you'll see pipe banging and stressed fixtures) or restricting too much (low pressure everywhere). Replacement is $400-800 and is one of the most common fixes we do for whole-house low pressure.
Cause #3: Partially closed main shutoff
Sometimes the main water shutoff valve was partially closed during prior work and never fully reopened. Free fix if you're comfortable working with the valve. Check that the lever or handle is fully in the open position. If the valve is corroded or won't move, that's a $250-400 valve replacement.
Cause #4: Aging galvanized supply lines (the big one)
This is the cause we see most often in homes built before the 1960s in places like Lexington Center, Wedgemere in Winchester, Stoneham Center, and older parts of Woburn. Galvanized steel supply lines were the standard for decades, but they rust from the inside over time, gradually narrowing the pipe interior. A 1" supply line can end up with a 1/4" interior diameter after 60 years. The result: weak flow especially on the second floor and at any faucet far from the main. Fix is partial or full repipe with copper or PEX — $3,000-$15,000+ depending on home size and accessibility.
Cause #5: Municipal supply pressure variations
Less common but real. Some streets in older parts of Greater Boston have municipal water mains that drop pressure during peak morning and evening hours. If your low pressure is time-of-day specific, it might be a supply-side issue. We can install a booster pump ($1,500-$3,000 installed) to compensate.
Diagnosing which one you have
We start with the cheapest possible checks (aerators, individual fixtures), then test whole-house pressure with a gauge at an outdoor spigot, then check the PRV reading, and finally inspect supply lines visually where accessible. The whole diagnostic visit takes about an hour and we tell you which fix you need before quoting it. We don't sell repipes to people who need a $5 aerator cleaning.
Frequently Asked Questions
What is normal water pressure for a house?
Most residential systems should sit between 45-75 PSI. Below 40 feels noticeably weak; above 80 can damage fixtures and stress pipes.
Why is the pressure only weak on the second floor?
Almost always a supply-line restriction between the basement and second floor. Most common cause is galvanized pipe that's rusted closed on the upstairs run. Can usually be fixed by replacing that section.
Can low pressure damage anything?
Generally no — low pressure just means weak flow. It's annoying but not dangerous. High pressure (over 80 PSI) can damage fixtures, water heaters, and appliances over time.
How much does it cost to replace galvanized pipes?
Partial repipe (just the worst sections): $2,500-$5,000. Full house repipe: $6,000-$15,000+. Depends heavily on accessibility and house size. We'll always look at partial repipes first when they make sense.
Should I get a pressure booster pump?
Only after ruling out fixable causes. Boosters mask the symptom rather than fix the underlying problem and add complexity (and a thing that can fail). We recommend them only when the actual cause is supply-side, not fixable on the customer's side.
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