A common question that clients ask during home inspections is: “Does this house have good water pressure?” When you’re searching the housing market and touring homes, it’s important to look for a few key indicators of the home’s water pressure and how those systems are functioning.
What you usually want to know is whether the flow from the showerhead will be strong enough for a quality shower and whether someone flushing a toilet will interrupt that shower. Inadequate pressure can also affect other home appliances like dishwashers and washing machines, as well as sprinklers and other exterior landscaping systems that use water. These questions can’t be answered by examining water pressure on its own. Instead, we have to look at both water pressure and the resulting functional flow.
What is water pressure?
Water pressure is the amount of force from the water main into your home. It is measured in pounds per square inch (PSI), and normal water pressure is typically between 30 and 80 PSI.
What is functional flow?
Functional flow is the volume of water flowing through your pipes and arriving at individual fixtures. Poor functional flow may be due to buildups in the pipes or poor plumbing.
How to Test a Home’s Water Pressure
To determine whether a home has enough functional flow, go to the bathroom and turn on the sink and the shower. Wait for satisfactory water temperature in the shower and then flush the toilet. See if the flow diminishes. You can go to other fixtures and run the water too, but at some point, every system will experience diminished flow if you open too many fixtures at once. One sure way to kill the flow is to open up an exterior hose bib during testing. Keep it simple and test flow by opening up every fixture in a given bathroom.
You can also test your water pressure using the cold water supply faucet at your washing machine. To do this, screw a pressure gauge onto the faucet behind the washing machine (you’ll need to disconnect the hose before doing this). Turn on the faucet all the way and observe the pressure gauge to determine if the home is at the sweet spot.
How to Obtain Perfect Water Pressure
You don’t want your home to have water pressure that is too low, but water pressure can also be too high. Piping systems are designed to have no more than 80 PSI. When you exceed this pressure it can cause problems. High pressure will rarely cause pipes to burst, but it stresses the weak links in your piping system such as rubber hoses and gaskets, making them vulnerable to leaks and failure.
A pressure-reducing valve can correct high pressure. Below the valve is the main water shutoff. You can correct high residential water pressure by installing a pressure reducing valve. This is a bell-shaped device that reduces water pressure. Aim for water pressure that is 60-70 PSI.
If the house has low pressure, you first want to determine if the house is on a public water supply system or a private well system. Most public systems are required to deliver a minimum of 30 PSI to your house, so inadequate pressure on public water systems is rare.
If the house is on public water supply and the utility cannot improve your pressure, the solution involves installing a pressure tank and a pump. This gives your supply piping system a pressurized boost.
If the house is on a private well, poor pressure could indicate a problem with the captive storage tank and/or the pump and you should have the well system serviced by a qualified well expert.
Flaws in the Functional Flow
Rusted pipes can block water flow. Poor functional flow can be an issue in old houses with galvanized steel pipe. This type of pipe was commonly installed until the late 1960s and early 1970s. This pipe was manufactured with a coating of galvanization that was designed to prevent corrosion of the steel pipes. When this galvanization wears off, the pipes occlude with rust. The result is a restricted piping system that will not deliver adequate water to the fixtures even with all the pressure in the world. To fix the problem, you’ll need to replace the pipes.
Another common cause of poor functional flow is unprofessional water piping systems. Good plumbers know how to size the pipes correctly so that adequate water is delivered to each fixture. An amateur mistake is running too many fixtures off of pipes that have too small a diameter. The result is inadequate water supply to fixtures or poor functional flow. This can be difficult to repair without piping replacement.
Just because a fixture has poor flow, don’t assume anything about the pipes yet. Other factors in the piping system can result in poor flow. Sometimes an angle stop (one of those shutoffs below the sink) may be partly closed. Fixture aerators (the little screens inside the faucets) can become restricted. The main water shutoff to the house could be party closed or restricted. Supply connector hoses could be kinked or restricted.
I hope this clears up some common misconceptions about water pressure and functional flow. Remember, informed homebuyers are happy homebuyers.