Low Water Pressure at Home: Simple Tests Before You Re-pipe
The short version
Master plumber Jim explains the difference between water volume and pressure and how to troubleshoot low water pressure in a house. He covers a bucket flow test, removing aerators and shower heads, checking pipe size and corrosion, hot-side blockage and bypassing a water softener, before deciding whether re-piping is needed.
Full written account
Low water pressure in a house can mean a re-pipe, but master plumber Jim, who says he has 48 years in the trade, describes several cheaper checks to run first. He is a master plumber in Michigan and holds a C-36 plumbing contractor license in California.
Volume and pressure are different
Jim separates two things: volume, which is the size of the pipe and how much water it can serve to the house, and pressure, which is how much a pump or the city can give. A city normally gives about 40 pounds on average. In his area some houses can get as much as 250 pounds; his incoming pressure is about 140 pounds, which he reduces to 60 pounds or it would wreck his faucets.
Measuring flow
For a house on a well, he suggests timing a five-gallon bucket filled from a garden hose. One minute means five gallons a minute; half a minute means 10 gallons a minute. Five gallons a minute he calls pretty good flow. Modern faucets flow less than a gallon a minute and toilets flush on 1.2 gallons. He also suggests filling the bathtub from the shower to judge volume.
Aerators and shower heads
Take the aerator off and see whether flow improves. Shower heads can be low flow too, and lime can plug an aerator or shower head, which is an easy fix to clean. If flow is still low with the aerator off, it is a piping problem. If one faucet flows well and another does not, suspect that faucet or its supply lines.
Pipes
Older houses were often plumbed in half-inch copper, and some in galvanized pipe that is getting old and may be corroded inside. A half-inch line into the house is too small, he says. A city usually mandates at least three-quarter inch or one inch, and a newer well will have a one-inch pipe. Depending on water need it could be as much as an inch and a half. He says he has not really seen corrosion inside copper.
Hot side and water softener
If cold flows well but hot does not, he says electrolysis can start blocking the hot side, and he recalls finding debris plugging hot-water pipes. An aging water softener can also slow flow: bypass it, and if pressure is suddenly good, that is the problem.
When buying a house, he suggests turning on the shower to test the pressure. If pressure is low, the choice is to re-pipe or live with it.
Questions this video answers
How can I check my water flow at home?
Fill a five-gallon bucket from a garden hose and time it. One minute means five gallons a minute; half a minute means 10 gallons a minute. Five gallons a minute is described as pretty good flow.
How do I tell if the aerator or shower head is the cause?
Take the aerator off the faucet or the shower head off and see whether the flow improves. If flow is still low with the aerator off, it points to a piping problem.
What causes low water pressure in a house?
Plugged aerators or shower heads (lime), corroded galvanized pipe, undersized pipe such as half-inch, clogged hot-side pipes, a small well, or an aging water softener.
How do I check if the water softener is the problem?
Bypass the water softener. If pressure becomes good, the softener is the problem.
Do I have to re-pipe the house?
Re-piping is described as expensive. The video suggests troubleshooting first, then deciding whether to re-pipe or live with it.
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