Low water pressure in your house: causes and fixes

Why is my water pressure low?

Water pressure is low because something between the city’s main and your tap is restricting the flow, or because the supply itself has dropped. The first question is how much of the house is affected.

• One tap or shower: the problem is in that fixture.
• Hot water only: the problem is at or near the hot water tank.
• Every tap, hot and cold: the problem is at the main shut-off, the pressure reducing valve, the service line or the city supply.

Why is my water pressure low all of a sudden?

A sudden drop through the whole house usually comes from outside it. The City of Burnaby says heavy water use nearby, such as lawn watering, a broken water main or an open fire hydrant, can cause temporary low pressure.

Check with a neighbour. The City of Vancouver tells residents to request a City crew when pressure drops suddenly in the whole home and several neighbours are affected too.

If the neighbours are fine and the pressure doesn’t come back, Burnaby says the cause may be your plumbing or your pressure reducing valve. Also check that nobody has partly closed the main shut-off, which sometimes happens after other work in the house.

Why is the water pressure low at only one tap?

At a single tap, the usual cause is a clogged aerator. The aerator is the small screen on the end of the spout, and it collects grit and scale. Unscrew it, rinse it and try the tap again.

If that doesn’t help, check the shut-off valves under the sink, which may be partly closed, and the flexible supply lines, which can kink. A worn cartridge inside the faucet will also choke the flow. Vancouver’s guide lists low pressure at only one faucet or fixture as a plumber’s job, not a City one.

Why is the water pressure low in my shower?

Scale in the showerhead is the most common reason. Unscrew the head and soak it in vinegar, or replace it. If the pressure is still weak, the cartridge in the shower valve may be worn or clogged with debris. That often shows up after the water has been shut off and turned back on, because the surge knocks loose scale into the valve.

Why is the pressure low on hot water only?

If the cold side is strong and the hot side is weak everywhere, look at the hot water tank. The valve on the cold inlet above the tank may be partly closed, or sediment and scale may be restricting the outlet. On older houses with galvanized steel pipe, the hot lines often rust shut before the cold ones.

Why is the water pressure low in the house but fine outside?

That pattern usually points at the pressure reducing valve. On many houses the outside tap is piped ahead of that valve, so it runs at street pressure while everything indoors goes through the valve. When the valve fails or clogs, the house drops and the garden tap doesn’t.

What is a pressure reducing valve, and how does it fail?

A pressure reducing valve is a bell-shaped brass valve on the main water line, usually just after the main shut-off. It brings the pressure from the street down to a level that is safe for your pipes, tank and fixtures.

These valves wear out. Burnaby notes that a malfunctioning pressure reducing valve can cause high pressure, and that persistent low pressure can also trace back to it. Signs include:

• Pressure that is fine at one tap but collapses when a second one opens.
• Pressure that swings from weak to strong through the day.
• A humming or chattering sound from the valve.
• Banging pipes and taps that spit when first opened, which suggest pressure is too high.

Replacing the valve is a plumber’s job, and the new one should be set with a gauge.

Could a leak be causing low water pressure?

Yes. A leak in the buried service line between the street and the house bleeds off pressure before the water reaches you. Look for a wet patch in the yard that never dries, or the sound of water running when everything is off.

If you have a water meter, use it. Turn off every tap and appliance, then watch whether the meter still moves. The City of Surrey has videos that show how to check for a leak this way.

Do old pipes cause low water pressure?

They do. Galvanized steel pipe rusts on the inside as it ages, and the rust narrows the opening until less water gets through. The pressure fades over years, and the first water of the morning may run brown. Cleaning doesn’t fix it. The pipe has to be replaced, either the service line, the pipes in the house or both.

Who do you call for low water pressure, the city or a plumber?

Call the city if your neighbours have the same problem, and a plumber if it is only your house. Vancouver notes that the City is responsible for providing water up to the property line, and asks owners to check for causes on their own property before calling.

If your house alone has low or no pressure, Vancouver’s guide lists both a City crew and a plumber as options. Keep in mind that the City may charge for a service call when the cause is on private property. In Burnaby, the City says to hire a plumber or ask for City staff to check the supply coming into your property.

Is high water pressure a problem too?

Yes. High pressure wears out tap washers, toilet fill valves, supply hoses and the hot water tank, and it makes pipes bang when a tap closes quickly. Burnaby says a malfunctioning pressure reducing valve can cause it. Vancouver lists sudden high pressure as a reason to call a plumber.

When to call a plumber

Call a plumber when:

• Pressure is low at every tap and your neighbours’ water is fine.
• Pressure drops whenever a second tap is opened.
• There is a wet patch in the yard, or the meter moves with everything off.
• The water runs brown and the pressure has faded over time.
• Pipes bang or taps spit, which points to pressure that is too high.

DrainX finds and repairs leaks in water service lines, works on pressure reducing valves and main shut-offs, and repipes houses where old pipe has rusted narrow. Tell us whether the problem is at one tap or all of them, and whether it came on suddenly.