Water Pressure Explained: Bars, Flow & Fixes
Water pressure conversations run on two confused quantities: pressure (the push, measured in bar) and flow (the delivery, litres per minute) — and a satisfying shower needs both. UK suppliers must deliver a minimum head of pressure to your boundary, but what reaches your taps depends on your supply pipe, your system type and your fittings. Untangling which quantity you're short of is the whole diagnostic game.
Pressure vs flow, in one minute
Pressure is stored push — what the gauge reads with no water moving. Flow is what actually arrives when a tap opens, and it's flow you experience. High pressure with poor flow (a narrow or furred supply pipe strangling delivery) is common; so is adequate flow at low pressure (gravity systems). The jug test measures flow: time a tap filling a measuring jug and convert to litres/minute — under 10 L/min at the kitchen cold is poor, 10–15 fair, 15+ good.
Suppliers' obligation is pressure at the boundary (7m head minimum, roughly 0.7 bar, with most areas seeing 1–3 bar); inside the boundary is your infrastructure's job.
What sets your ceiling
System type first: gravity-fed homes make upstairs pressure from tank height (often ~0.1–0.3 bar at a shower — the eternal weak upstairs shower); mains-pressure systems (combi, unvented) deliver street pressure everywhere, so their ceiling is the incoming main. The supply pipe is the usual mains-side villain: Victorian lead or narrow old pipe, long shared supplies, and internally furred pipe all throttle flow regardless of street pressure.
Then the retail layer: quarter-closed stopcocks, standard-pattern isolation valves on shower feeds, furred hot-side pipework, scaled cartridges and clogged aerators each shave a little — and stack.
Fixes by price
Free tier: open the stopcock fully (then back a quarter), clean aerators and shower heads, check isolation valves are fully open. Cheap tier: swap restrictive valves for full-bore on shower runs, descale or replace scaled cartridges, right-size the shower head. Middling: shower pump on gravity systems (£400–£800 fitted — transforms tank-fed showers; not permitted on mains), or re-route/renew restrictive internal pipework.
Structural tier: replace the supply pipe (£1,000–£3,000+ — the fix for whole-house poor flow on old/narrow/lead supplies, with moling techniques avoiding trench drama), convert to mains-pressure hot water (unvented, subject to the main measuring up), or — for genuinely weak mains — accumulator/pump-and-break-tank solutions that store and boost within regulations. The measurement dictates the tier: fixing retail restrictions under a strangled supply pipe polishes the wrong thing.
Too much of a good thing
Pressure above ~4–5 bar hammers appliances, weeps at joints, erodes tap washers and makes systems noisy — common at night (network pressure rises as demand falls) and in low-lying streets. The fix is a pressure reducing valve (PRV) on the incoming main, £150–£300 fitted, often set around 3 bar; unvented cylinder installations include one as standard.
Symptoms that point here: banging pipes at night, repeatedly failing fill valves and tap washers, and dramatic splash-back at basins. One PRV settles all of it.
| Symptom | Short of | First fix |
|---|---|---|
| Weak upstairs shower, gravity system | Pressure (head) | Pump or system change |
| Whole house weak, all times | Flow (supply pipe) | Supply pipe survey |
| One outlet weak | Local restriction | Aerator/valve/cartridge |
| Weak at peak times only | Network/shared supply | Log & report; accumulator |
| Bangs, splashy, valves failing | Excess pressure | PRV |
Renters, landlords and shared responsibility
Prevention splits sensibly across a tenancy: tenants own the behavioural layer (reporting drips promptly, not flushing the unflushable, basic frost sense) while landlords own the structural one (valves that work, hoses replaced on schedule, systems serviced). Both sides benefit from the same checklist — and landlords who fund the preventive visit reliably spend less than those who fund the emergencies it would have prevented.
Frequently asked questions
What water pressure should a UK home have?
Suppliers must provide at least 7m head (~0.7 bar) at the boundary; 1–3 bar is typical in practice. Indoors, 1–2 bar working pressure with 12+ L/min flow runs a home comfortably; mixer showers like 1 bar+; some fittings specify minimums worth checking pre-purchase.
Can I fit a pump to boost my mains pressure?
Not directly — regulations cap what you may draw from the main by pump. Compliant boosting uses a break tank or accumulator arrangement. On gravity (tank-fed) systems, ordinary shower/whole-house pumps are fine and effective — the tank is what makes them legal.
Why is my hot pressure worse than my cold?
The hot side has travelled further through more restriction: cylinder circuits, older pipework, scale (hot pipes fur fastest), and on gravity systems the tank-height limit. Mains-pressure cold beside gravity hot is the classic mismatched-shower cause — balancing the two is a design job.
My flow halved recently with no changes — what happened?
Recent-change flow drops point at: a partially closed/failing stopcock, a leak (check the meter still-test), a collapsing supply pipe, or — after any works — grit in strainers, valves and cartridges. Sudden beats gradual for diagnosability: note the date and call it in.
Where this guide's advice ends
Written guidance has a natural limit: it can tell you what usually causes a symptom, but only eyes on your actual pipework can confirm it. If what you're seeing doesn't quite match any pattern described here, or matches several at once, that ambiguity is itself diagnostic information worth giving an engineer. Our vetted local plumbers do this triage daily — and an honest one will tell you on the phone if your problem sounds like a cheap fix, a bigger job, or (occasionally) not a plumbing problem at all.