What's so important about water pressure anyway?

Home buyers are often concerned about the water pressure at a home they plan to purchase. On the other hand, to complicate matters, it seems that no two home buyers agree on what is satisfactory water pressure. Realizing that, home inspectors try to provide their clients with a water pressure reading that they can analyze and evaluate on their own.

Home buyers often ask the home inspector about the water pressure at a prospective property. Is it good? Is it bad? Or my favorite, “The water pressure seems really low in the master bathroom upstairs…” Unfortunately, water pressure is pretty much subjective. What one person thinks is great pressure could be a mere trickle to another person. Those people who are used to obtaining their water from private wells are often less critical of water pressure than those individuals who are accustomed to getting water from sophisticated municipal water systems. Water pressure also can become a critical issue with so many contemporary American homes having relatively large five-piece master bathrooms, often on a second or third floor which further complicates the water pressure issue.

Since water pressure is largely subjective, the best thing to do is to measure it so you can decipher and evaluate the numbers themselves. There is a device known as a water pressure gauge. This portable meter screws onto an outside hose bibb, or inside at the laundry area, and gives a homeowner, a plumber or a home inspector an accurate pressure reading of the plumbing distribution system at a given property. Normal water pressure is in the range of 60 to 80 pounds per square inch (PSI) with an additional common range for rural properties (wells) running between 40 to 60 pounds per square inch (PSI). This water pressure gauge can yield a pretty accurate reading although, during the day, it could change a bit depending on the number of fixtures that are being operated and other variations that affect overall water pressure. My practice is to measure the water pressure when none of the fixtures are being operated (typically one of the first things I do at a property before anyone shows up for the inspection).

Water pressure at or below 40 PSI, while not uncommon to find, usually means there is not much pressure to spare if more than one fixture or appliance is running at a time; for example, trying to shower while the dishwasher is running could be an ordeal. Water pressure above 80 PSI is not good for household appliances -- washing machines, dishwashers, and hot water heaters. Consistently high water pressure can damage or significantly shorten the design life of these and other household appliances. The more common victims of high water pressure are washing machine hoses and water inlet valves on dishwashers and washing machines. Now if your water pressure is too high to start with, say 110 PSI and someone slams a valve closed quickly, the water hammer can exceed 200 psi, which is more than enough to burst conventional distribution piping. I you are buying a home, your home inspector should check and report the water pressure for you (check your inspection report to make sure). If, on the other hand, you are merely a curious consumer who wants to investigate this matter by yourself, an accurate but inexpensive water pressure gauge can be purchased at almost any hardware store.