Low water pressure has a long list of possible causes, from a clogged aerator to a leak in the line under your lawn. Three quick questions cut that list down to a handful.
- Is it one fixture, or the whole house?
- Is it hot water only, cold only, or both?
- Did it drop suddenly, or fade over months?
One fixture or the whole house?
Just one fixture
If only one tap or shower is weak, the problem is almost always at that fixture. Start with the aerator (the small screen at the end of the spout) or the shower head. Sediment collects there, especially after work on the water main stirs up the pipes. Unscrew it, rinse it, and try the tap without it.
If the tap is still weak with the aerator off, look further back: a shut-off valve under the sink that isn't fully open, a kinked or failing supply hose, or a worn cartridge inside the faucet. A single-handle faucet that gives plenty of cold but little hot, or the reverse, usually has a cartridge problem.
The whole house
When every fixture is weak, the cause is upstream of all of them: the main shut-off, a pressure-reducing valve, the pipes themselves, a leak, or the municipal supply.
Hot only, cold only, or both?
Low pressure on the hot side only points toward the water heater: a valve at the tank that isn't fully open, sediment in the tank or its connections, or a fault in a mixing valve. Our water heater repair page covers that side. Low pressure on both hot and cold points back to the supply.
Sudden drop or slow decline?
A sudden drop usually has a cause you can track down.
- Work on the water main in your street, which your neighbours will be noticing too
- A main shut-off that was partly closed during other work and never fully reopened
- A pressure-reducing valve that has failed
- A leak, sometimes a large one, inside the house or on the service line outside
A slow decline over months or years is more often about the pipes themselves.
- Galvanized steel pipe, found in many older homes, corrodes on the inside and narrows until very little water gets through
- A pressure-reducing valve wearing out gradually
- Mineral and sediment buildup in valves and fittings
- A small leak that has been growing without anyone noticing
Older homes often have a mix of pipe materials from different decades. If yours also has Poly-B supply lines, our Poly-B guide explains what to watch for.
The pressure-reducing valve
Many homes have a pressure-reducing valve (PRV) near where the water line enters the house. It brings the municipal supply pressure down to a level household plumbing can handle. When a PRV fails it can go either way: pressure can drop, or it can creep so high that pipes bang when a tap is shut off and relief valves start to drip.
A PRV isn't something to adjust by feel. A plumber can put a gauge on an outside tap, read the actual pressure, and tell you whether the valve is doing its job.
Could it be a leak?
A leak takes pressure from everything downstream of it, and a leak on the service line between the street and the house can run unseen for a long time. If your home has a water meter, you can test for one yourself: make sure nothing in the house is using water, read the meter, wait an hour without running anything, and read it again. If the number has moved, water is going somewhere. Many meters also have a small dial or indicator that turns when even a little water is flowing. Our guides to hidden water leak signs and water bill spikes go into more detail.
Outside, watch for a patch of lawn that stays soggy when it hasn't rained, water bubbling up through the ground or a driveway joint, or the sound of running water with every tap off. Those point to the service line. We find those leaks with leak detection and fix them with water line leak repair, or with water line replacement where the line is past repair.
Is it the city, or your plumbing?
Ask a neighbour. If the whole street has low pressure it is almost certainly municipal, and your city's website will usually list water main work and service interruptions. In general the municipality is responsible for the supply up to your service connection and the homeowner for the pipe from there into the house, but where that line falls varies between cities, so check with yours before assuming either way.
What you can safely check yourself
- Clean the aerator or shower head on the weak fixture
- Make sure the shut-off valves under that sink are fully open
- Make sure the main shut-off is fully open. Turn old valves gently, because a seized valve can break if it is forced.
- Do the meter test for a leak
- Walk the yard looking for soggy patches, and listen for running water
If you don't know where the main shut-off is, our guide to finding your water shut-off shows the usual spots in Lower Mainland homes.
What a plumber checks
- Static and flowing pressure at an outside tap, measured with a gauge
- The pressure-reducing valve and the main shut-off
- The pipe material and its condition wherever it is exposed
- The water heater valves and connections, if the problem is on the hot side
- Leak detection on the service line, if the meter or the yard suggests a leak
That turns a vague problem into a specific one, and the fix follows from there.
Dealing with this right now? Mr. Plunger Plumbing & Drainage answers 24/7 across Surrey, Delta, Langley, White Rock, Richmond, Maple Ridge, Pitt Meadows, Vancouver and the rest of the Lower Mainland. Call (604) 870-1442 to talk to a real plumber, get an ETA before anyone is dispatched, and get a quote before any work starts.