A friend recently sent me a link to an article on The Onion titled “Realtor Was Not Expecting Such Hard-Hitting Questions About Water Pressure”.   The Onion is an online satirical news website. None of their articles are actual news, but the satirical nature of their articles often highlights some uncomfortable truths.   I had a good laugh reading this article because I get the same questions from home buyers frequently.  The concerns expressed by the home buyer in the article are commonly referred to as “functional flow” by home inspectors. How does a home inspector evaluate water flow?

Water Pressure

A home inspector will observe the home’s water pressure by connecting a gauge to an outdoor spigot. Water pressure should be between 40-80 PSI.   If water pressure is too low there can be issues with flow and if it is too high it can place stress on flexible hoses and appliances.  Having satisfactory water pressure does not guarantee that  all fixtures in the home will have adequate water flow.  Additional testing is required.


Functional Water Flow

During the home inspection, an inspector will run multiple fixtures (sinks, tubs & toilets) at the same time to determine if the water supply system has adequate capacity.  These tests are to observe the home’s functional water flow.   I have observed homes with a static water pressure of 80 psi that dropped to less than 20 psi when multiple fixtures were operated.    The shower slowed to a trickle when the toilet was flushed. This home had a restriction somewhere in its water supply line.  Does this have to be fixed? Well…. I couldn’t live with it. It was a deal breaker for the buyer. However, the current owners were living with it.

Another situation I encountered was a new construction condo that had 40 psi water pressure at ground level. This was a 3 story building. Water pressure decreases by 0.4 psi for ever 1′ increase in elevation.  Assume the 3rd floor shower head is 25′ above the ground. This would drop the water pressure to around 19 psi. Which is low.  All the 3rd floor fixtures did well on the functional flow test. They were not affected by other fixtures being operated. The only problem was the flow levels were noticeably low.  The builder had even fitted low flow aerators and shower heads.  The buyers visited at the end of the inspection and I was able explain the low pressure situation.  They observed the low flow of the fixtures on the 3rd floor and were not concerned.

In summary, water pressure is a starting point for evaluating a water supply system, but meaningless without testing functional flow. Also, buyers should always attend the home inspection. Inspectors do their best to write reports that objectively present all the issues with the house.  Seeing “low water pressure” in the inspection report can really upset a buyer. If they get a chance to actually observe the flow they can determine if it meets their needs.