Why is my water pressure low?

Weak pressure at a tap or shower is one of the most common calls we get, and it is worth ruling out the cheap, common causes before assuming the worst. In that order, from cheapest to most involved:

A scaled shower head or tap aerator

London’s water is hard, and limescale builds up inside the small holes of a shower head or tap aerator over months, restricting flow without it being obvious from the outside. Unscrewing and soaking one in descaler, or simply replacing it, is a five-minute fix that solves a surprising number of "low pressure" complaints.

A partly closed valve somewhere on the run

An isolation valve left slightly closed after previous work, or a stopcock that has never been fully opened, restricts flow to everything downstream of it. Worth checking the main stopcock (usually under the kitchen sink) and any isolation valves near the affected fixture are fully open.

Only the shower is weak, not the taps

If every tap in the house is fine but specifically the shower is weak, that narrows it considerably. On a system fed from a cold water tank, the answer is often a shower pump. On a combi or mains-pressure system, a pump cannot help — a pump boosts a gravity-fed system’s pressure and cannot be fitted to a mains-fed one, so if that is your setup the cause is elsewhere on that specific run.

An old or undersized supply pipe

In older London housing stock, the supply pipe running from the street was often sized for the water demands of decades ago — a single bathroom, not a house with an en-suite and a utility room added since. Modern combined demand from several outlets at once can outstrip what an old, narrow lead or undersized pipe can deliver, and this is the one cause on this list that needs the pipe itself looked at and potentially upgraded, covered under general plumbing.

Pressure dropped suddenly, everywhere

A pressure loss that arrived suddenly and affects the whole property, rather than something that has been gradually weak for years, is a different situation — that pattern is more consistent with a leak somewhere on the supply than an undersized pipe. See leak detection if that sounds like what you are seeing.