Water Pressure Problems: Why It Drops and What Fixes It
Weak showers and slow-filling baths get blamed on pressure, but pressure and flow are different things and the distinction decides the fix.
Weak showers and slow-filling baths get blamed on pressure, but pressure and flow are different things and the distinction decides the fix. Pressure is the force behind the water; flow is how much of it actually arrives per minute. A property can have perfectly good pressure and poor flow, and no amount of pump or cylinder will help if the constraint is a partially closed valve or a furred-up section of pipe.
Pressure versus flow rate
Static pressure is measured with everything closed and tells you the force available. Dynamic flow rate is measured by timing how long a known volume takes to fill with an outlet fully open, and tells you what the system can actually deliver. Poor flow with good static pressure almost always means a restriction — a part-closed stopcock, an old lead or narrow-bore supply, a blocked filter, or scaled pipework. Poor pressure and poor flow together usually points upstream to the incoming main.
Whole-house or single outlet
If every outlet is weak, the problem is at the incoming main, the stopcock, or a whole-house filter or valve. If one outlet is weak, it is that outlet: a blocked aerator, a scaled cartridge, a part-closed isolation valve on the tail, or a flexible connector that has collapsed internally. Checking a second outlet takes ten seconds and immediately halves the number of possible causes.
Gravity systems and why upstairs suffers
In a vented system fed from a loft tank, pressure at any outlet depends on the height of water above it. A shower on the top floor sits close to the tank and has little head, which is why it dribbles while the kitchen tap downstairs is fine. The answers are a pump correctly sized and installed, raising the tank where possible, or converting to a mains-pressure unvented system if the incoming flow supports it.
Combi boilers and hot water flow
A combi's hot water flow is limited by its kW output — it can only heat so much water so fast. In winter, incoming mains water is colder, so the same boiler delivers less hot water per minute at the same temperature. A weak hot flow that gets worse in winter and is fine in summer is often not a fault at all but the boiler working to its rating, which is a sizing conversation rather than a repair.
Sudden loss of pressure
A sudden change, rather than a gradual one, suggests something specific: work carried out by the water supplier, a burst on the main, a stopcock partly closed during other work, a failed pressure reducing valve, or a filter that has blinded. Check with neighbours first, because a supply-side issue affects the street and is the water company's responsibility rather than yours.
What can actually be done
Depending on the cause: replacing a restrictive or seized stopcock, upgrading the incoming supply pipe, descaling or replacing outlet cartridges and aerators, fitting a correctly specified pump on a gravity system, installing an accumulator where mains flow is limited but storage can smooth peaks, or moving to an unvented cylinder where the main can support it. The measurement comes first — specifying equipment before measuring flow is how people end up with expensive kit that changes nothing.
Weak showers or slow-filling taps
Tell us whether it is one outlet or the whole house, and hot, cold or both, and we will work out whether it is pressure or flow.
Questions we get asked
Is low pressure the water company's problem?
It can be. Suppliers have a minimum pressure obligation at the boundary. If the whole street is affected, start with them before paying for work on your side.
Will a pump fix my weak shower?
On a gravity-fed system, often yes with the right pump correctly installed. On a mains-fed or combi system, pumping the mains is not permitted and is not the answer.
Why is my hot water weaker in winter?
Incoming water is colder, so a combi has to work harder to reach the same temperature and delivers fewer litres per minute. It is usually the boiler's rating, not a fault.
Can old pipework reduce flow?
Yes. Narrow-bore, lead or heavily scaled supply pipework restricts flow regardless of how good the pressure at the boundary is.
How do I measure flow rate myself?
Open a cold tap fully, time how long it takes to fill a container of known volume, and convert to litres per minute. It is rough but genuinely useful.