How to diagnose residential high or low water pressure

By Fred Bretzke

Pre-manufactured water hammer arrestors.

We regulate the water pressure in single-family residences to a maximum of 80 PSI or 550 kpa, according to ( 1) of the NPC Static Pressure 1. Where the static pressure at any fixture may exceed 550 kPa, a pressure-reducing valve shall be installed to limit the maximum static pressure at the fixture to 550 kPa.

Most homes have approximately 60 to 65 psi, the reason being is that if it is more than 80 psi, some plumbing fixtures may fail from excessive water pressure or water hammer. To prevent water hammer in homes we used to install 1/2-in. air chambers extended on top of the bathtub water feeds in the wall. This is no longer recommended with the availability of water hammer arrestors.

A- Water Hammer Prevention. Water hammer is a buildup of pressure in a length of horizontal or vertical pipe that occurs when a valve or faucet is closed suddenly. The longer the pipe and the greater the water velocity, the greater the pressure exerted on the pipe, which can be many times the normal static water pressure and be sufficient to damage the piping system. Since air chambers made from a piece of vertical pipe do not provide acceptable protection, pre-manufactured water hammer arrestors are required to address this potential problem. Water hammer arresters need not be installed at every valve or faucet, nor in every piping system.

How do we diagnose pressure problems with fixtures? These will fail first if pressure is too high:

  • The ballcock in the toilet tank will start vibrating and bang when it shuts off.
  • The dishwasher, which has a solenoid valve in it to shut the water off suddenly, will begin to water hammer or bang when shutting off.
  • The clothes washing machine, which also has a solenoid valve in it to shut the water off suddenly, will begin to water hammer or bang when shutting off.
  • Some taps will start to need maintenance.
  • Vibration in copper waterlines may also happen, usually PEX plastic lines don’t vibrate, but their joint rings could blow.

How do you solve it?

Check the pressure at the outside hose bib by attaching a 0-100 psi pressure gauge. If indeed the pressure exceeds 80 psi, install a pressure reducing valve on the main supply just after the water meter, which should include a pressure gauge to monitor if your pressure is too high or if you have an internal leak.

The flipside: Low pressure

As per code 5) b) the minimum water pressure at the entry to the building is 200 kPa, or 28 psi. It states in the code that 28 psi is the lowest pressure allowed. This is because they now manufacture toilets that require a minimum of 22 to 25 psi.

If the homeowner only has 28 psi pressure in their urban or rural house they will be an unhappy camper; 28 psi is not adequate, your client will want more. What is wrong when the pressure is too low?  Let’s talk about houses with wells first.

Shallow Well Pumps (25 ft.)

There are basically two types of pumps for water wells now. Back in the day, people use to hand dig wells up to 25 ft. deep. This is because hand pumps could overcome atmospheric pressure to suck water out of the well. Practical lift for pumps is the equivalent of 25 ft., while theoretical lift is about 34 ft. without pipe loss.

I remember when I was a kid in 1965, my dad and his brother hand digging a 25 ft.-well on a hot summer day near Ottawa. I remember it was extremely humid, as my uncle cursed in English and German and they smoked cigars and drank their Labatts stubby cold beers.

After they completed the well, we rejoiced with cold water from the hand pump and carried it into the farm house. It was a simple system but about 10 years later they installed a single pipe jet pump, which was then a luxury of 30 to 40 psi pressure in the freshly plumbed house.

Single pipe jet pumps are easy to fix but a little noisy in the house. The main problem if the pressure is low, is a plugged foot valve (vertical screened check valve) at the bottom of the well. You need to pull it, clean it or replace it.

Deep well pumps (over 25 ft.)

Two pipe jet pumps allow you to go a bit deeper underground, 60 to 90 ft. depending on the design. They still have foot valves, which could plug with mud as the aquifer may run dry.

The most common deep well pump is a submersible pump. These pumps can go several hundred feet deep. They do not have a foot valve on the bottom of the deep drop pipe. They have only one drop pipe, which is lowered down in a well casing until it hits a deep aquifer of clean underground water. This water is the best as it has been filtered through several hundred feet of the ground minerals. The stainless steel screened pump is tied to the bottom of PPE series 160 pipe and lowered into the aquifer of water. They usually last 15 to 20 years and you never hear them as they are underground.

Water pressure is usually regulated with a pressure switch, which has a differential of 20 psi. For example, a 30 to 50 psi or 40 to 60 psi cut in and cut out switch. If you run low on water pressure it could be undersized, the diaphragm pressure tank could have a integral split diaphragm, or there could be a hole in the drop pipe.

City water pressure too low

If the toilet pressure is too low, it might just need the rim holes around the bowl to be cleaned of calcium build up (a coat hanger works great). The ballcock may be plugged and may need replacing. Aerators or faucet screens may need replacing or cleaning. The hot water tank may have too much calcium build up on the bottom of the tank. You may have to drain it and try and reverse flow through the hose bib drain valve on the bottom. If this isn’t done every year, it’s usually a waste of time.

If the house is really old with galvanized water lines, those lines are likely plugged with rust and will need replacing. Rarely but sometimes the main shutoff may not be fully open. Sometimes there is actually a leak under the house, inside or outside, then you need to leak detect it. Let’s hope it’s not an underground outside leak as most insurance companies will only cover it if it’s under the house.

Finally, people don’t realize how much they rely on water until they are out of it. Remind your customers of preventive approaches.


Fred Bretzke is a full-time pipe trades instructor with Calgary’s SAIT Polytechnic and the recipient of the 2024 Cadmus Teaching Chair. Fred also received the 2020-2021 Innovation of The Year Award: SAIT for digitizing the project-based learning approach apprenticeship training is known for. He can be reached at [email protected].


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