Low Water Pressure in the House: Causes and Checks
When every tap is weak, not just the shower, the cause is usually the stopcock, the supply, a leak or old pipes.
Low water pressure throughout a house is usually caused by a stopcock that is not fully open, a problem with the water company's supply, a hidden leak, or old lead or iron supply pipes narrowed inside. Check the stopcock first, then ask neighbours and check Thames Water's postcode service page.
Published 28 September 2026 · Written by the Emergency Plumb engineers
Why is the water pressure low in my whole house?
Low water pressure in the whole house usually has one of four causes: a stopcock that is not fully open, a problem with the water company's supply, a hidden leak, or old supply pipes narrowed inside by rust or scale. Check the stopcock first, because it is free and takes a minute. If only the shower is weak and the taps are fine, see our separate guide to low water pressure in a shower instead.
Has it dropped suddenly or gradually?
This is the most useful question to answer first. A sudden drop, where the pressure was fine yesterday and weak today, points to something that changed: a supply problem in the street, a stopcock someone has turned, or a new leak. A slow decline over months or years points to something that builds up: old iron pipes rusting inside, limescale in fittings, or a filter or softener slowly clogging. Knowing which it is saves a lot of guessing.
Is your stopcock fully open?
Find your internal stopcock. In most London homes it is under the kitchen sink, but it can be under the stairs, in a cupboard or under a floorboard near the front door. Turn it anticlockwise as far as it will go, then back a quarter turn so it does not stick. It is very common for a stopcock to be left half closed after building work or a repair. If it will not turn at all, do not force it with a wrench, because old stopcocks can snap. Also check any other valves on the incoming pipe, and if you have a water meter, the valve next to it.
Is it a Thames Water supply problem?
Ask a neighbour or two whether their water is weak too. If it is, the problem is almost certainly in the water company's network, such as a burst main or repair work nearby. Thames Water supplies most of London and has a page on its website where you can enter your postcode to see current problems in your area. Pressure also dips at busy times of day, such as early morning, when a whole street is showering at once. If the problem is theirs, report it to them. There is nothing a plumber can do inside your house to fix a mains problem in the street.
Could a hidden leak be causing low pressure?
A leak on your supply pipe, underground or under a floor, lets water escape before it reaches your taps. Signs include a damp patch that will not dry, a hissing sound when everything is off, a higher water bill, or grass that stays unusually green along one line. If you have a water meter, turn off every tap and appliance, note the reading, wait an hour without using any water, and read it again. If the numbers have moved, water is going somewhere. Tracing and repairing a hidden leak is a fixed £280 to £600 with us, agreed in writing before we start.
Old lead or iron supply pipes
In many older London houses, the pipe bringing water in from the street is lead, or galvanised iron. Iron pipes rust inside, and the rust slowly narrows the bore until very little water gets through. Lead pipes are soft and grey, do not ring when tapped, and show a bright silver colour if you scratch them gently with a coin. Lead is also a health concern, because it can dissolve into drinking water, especially in pipes that stand unused overnight. The supply pipe from your property boundary to the house is usually the homeowner's responsibility. Replacing it with modern plastic pipe fixes both the pressure and the lead in one job.
Test your flow with a bucket and a timer
You can measure your water flow in a simple way. Take a bucket of a known size, such as a ten-litre bucket. Turn the kitchen cold tap fully on, because that tap usually comes straight from the mains, and time how long the bucket takes to fill. Divide the litres by the seconds and multiply by sixty to get litres per minute. Write the number down. It gives you something to compare against, whether with a neighbour's house, with the same test on another day, or after a fix. It is also useful information to give a plumber or Thames Water. While you are there, run the hot tap too. If only the hot is weak, the problem is more likely the boiler, the hot water cylinder or a blocked filter than the supply. And unscrew the aerator, the small mesh on the end of the spout, as limescale and grit collect there and can make a single tap feel much weaker than the rest.
When is a pump or an accumulator the answer?
Only once the causes above are ruled out. If your house has a cold water tank in the loft feeding the taps, low pressure upstairs is normal, and a pump can help, often just for the shower. If you are on mains pressure and the flow is fine when one tap runs but falls away when two or three run together, an accumulator may help. It is a tank that stores mains water under pressure and releases it at busy times. Fitting a pump directly on the incoming mains pipe is restricted under water regulations and needs the water company's consent, so do not buy one online and fit it yourself. We charge £110 for the first hour and £45 per extra half hour to investigate, with no call-out fee.
Low Water Pressure in the House: Causes and Checks, your questions
Why has my water pressure suddenly dropped?
How can I check my water pressure at home?
Who is responsible for low water pressure?
Can old pipes cause low water pressure?
Should I fit a water pump to boost pressure?
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