Causes of Low Water Pressure

The entry in brief

A single feeble tap nearly always has its own fault: a gritty aerator, a scaled shower head or a tired cartridge. When every tap is feeble, start with the main valve, the pressure regulator, old pipes, or a problem on the municipal side. Hot only? Then the water heater or its valves are the likely suspects.

What is going on

Water enters your home from the municipal main through a service line, passes the meter and main shut-off, then branches to fixtures. Anything along that path that narrows the opening reduces flow. Lake Ontario water carries minerals that settle into screens and valve seats. Older galvanized steel pipe rusts inward over decades. Partly closed valves, often left that way after some past repair, are surprisingly common.

On the city side, watermain repairs, hydrant flushing or a break nearby can lower pressure for a time, often with discoloured water.

In order

1. Check several fixtures, hot and cold, upstairs and down. Write down which ones are weak.
2. For a single tap, twist off the aerator, rinse the sand out, and give it a vinegar bath if it is crusted.
3. For a showerhead, remove it and clean the inlet screen and nozzles.
4. If the whole house is weak, check that the main shut-off is fully open.
5. Check for a bell-shaped regulator right after the main valve. A failing one can drop pressure sharply.
6. Ask neighbours whether they have noticed the same, and check the municipal water service updates for work on your street.
7. If only hot water is weak, check the valves at the water heater, and for a tankless unit, consider whether it is due for descaling.

Slips to avoid

• Cranking up a pressure-reducing valve without measuring. Excess pressure can damage fixtures and hoses.
• Replacing a whole faucet when only the aerator or cartridge is clogged.
• Ignoring a sudden drop. Gradual decline points to scale; a sudden one may mean a leak or valve failure.
• Forcing an old main shut-off that will not turn. It can break off in your hand.

When the ledger says phone

Call when cleaning the obvious screens does not help, when pressure is low throughout the house, when you suspect galvanized pipe, or when a valve will not turn. We test static and running pressure, check the regulator, and trace the restriction back toward its source, one section of pipe at a time, then write down what we found.

Not every fixture problem is pressure, though. A toilet that is slow to refill may simply need a new fill valve, as explained in our note on running toilet fixes.