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Low Water Pressure
Taps trickle, the shower is weak, or pressure drops away whenever someone else uses water.
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What's happening?
Pressure and flow are different things and homeowners usually mean flow — how much water actually arrives at the tap. Your supplier has a statutory minimum static pressure it must maintain at the boundary, but everything after the boundary is yours: the supply pipe, the stop tap, the internal pipework and the fittings. A whole-house drop points at the incoming supply or the stop tap. One weak tap points at that tap or its isolating valve. A gravity system fed from a loft tank gives naturally low pressure upstairs because the pressure is only the height of water above the outlet.
What usually causes it?
- Internal stop tap only partly open, or a washer inside it that has swollen and is throttling the bore
- Old lead or narrow-bore supply pipe from the boundary, restricting flow before it reaches the house
- Scale, grit or a blocked aerator in the tap spout or shower head
- A service isolating valve under a basin or sink knocked partly closed
- Shared supply pipe with neighbours, so pressure drops when several homes draw at once
- Gravity-fed system with the cold tank too low, or the tank's outlet partly blocked
- Pressure-reducing valve set too low or failing
Is it dangerous?
Low pressure is not dangerous on its own, but a sudden unexplained drop can be the first sign of a leak somewhere on your supply — a split underground pipe will show as poor flow long before it shows as a damp patch. A drop that appears overnight, alongside a jump in the water bill or the sound of running water with everything off, deserves investigating rather than living with.
Can I fix it myself?
Work through the cheap checks. Confirm the internal stop tap is fully open — turn it anticlockwise as far as it goes, then back a quarter turn. Unscrew the aerator on a poor tap and clear the mesh of grit and scale, and descale the shower head. Check the small isolating valves under basins and sinks are in line with the pipe, not across it. Ask a neighbour whether their pressure is poor too: if it is, it is a supply-side issue for your water company.
When should you call a plumber?
Call a plumber when the whole house is weak and the stop tap is fully open, when pressure has dropped suddenly with no explanation, or when you can hear water running with every outlet closed. Also call when an old lead or narrow supply pipe needs upgrading, or when a shower needs a pump or an accumulator to be usable. If pressure at the boundary itself is below the supplier's minimum, that is a matter for your water company.
What will the plumber actually do?
- Gauge static and dynamic pressure and flow rate at the internal stop tap to separate a supply problem from an internal one
- Check the stop tap and any pressure-reducing valve, and replace a throttling or failed valve
- Isolate sections to find a restriction, a partly closed valve or a leak on the supply run
- Clear or replace scaled fittings, aerators and shower valves
- Advise on upgrading an undersized or lead supply pipe, and notify the water supplier where required
- Size and fit a shower pump or accumulator where the incoming flow genuinely cannot support the outlets
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