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Plumbing 101: Low Water Pressure vs Low Water Volume


low water pressureI got a call from a customer that she were having a problem with her plumbing: low water pressure. This is a common description from homeowners that is used generically for many different water problems. In this case, the homeowner was complaining about whenever she showered, if someone turned on a faucet, the water would dramatically decrease in the shower to the point that she couldn't shower until that faucet was turned off. We see this happen with pressure balancing anti-scald shower valves to avoid someone getting scalded if, for example, someone flushes the toilet. This type of valve intentionally lowers the hot water pressure to keep the temperature constant when there is a sudden draw of cold water. That wasn't the case with this though. The problem was uniform throughout the house, and not just isolated to that particular shower.

People often misuse the term low water pressure. In this case, the water pressure was fine. We put a water pressure gauge on the hose bib and the incoming pressure was nearly 75 psi. This is considered very strong water pressure. The problem here was the water volume. You can have strong water pressure but poor water volume. The result is a weak shower.

The first thing to check is the main water valves. In this case we went to the street and the water meter was turned on only about halfway, effectively cutting the water volume in half. Simply turning the valve all the way to the open position solved this customer's shower issue.

Had this not solved her volume problem, we would have done more investigating starting with the shut-off valve in the garage. It happened to be a gate valve which has a reputation for causing problems, such as the gate breaking off and partially or completely blocking the flow of water.


This is great information to help people get the difference between low water pressure and low water volume.
Posted @ Friday, September 03, 2010 4:47 PM by The lonely hollywood plumber
There is so much ambiguity in regard to this topic. Pressure and volume are just some of the concepts we need to consider, especially when designing new custom showers.
Posted @ Saturday, March 05, 2011 12:43 PM by Douglas Nichols
Hey i like your post very much ! thanks for sharing this...High Pressure Water 
Posted @ Friday, January 18, 2013 12:22 AM by Marcus013
I have experienced low hot water volume over the past 10 or 12 months through out my 10 wear old home. (about 1 gallon per minute flow) The cold water has plenty of pressure and volume. Is it my water heater.
Posted @ Monday, February 24, 2014 11:41 AM by Gil Sims
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