Slowly Losing Water Pressure? It Could Be a Hidden Leak

Two Different Pressure Problems

Water pressure problems come in two forms: pressure that was always low, and pressure that has declined over time. They look similar at the tap but have very different causes. A pressure that was always low is typically a mains supply issue, an undersized supply pipe, or a PRV set too conservatively. Pressure that has gradually declined over months — particularly in a property where it was previously good — is a different problem and warrants a different investigation.

Gradual pressure decline is one of the classic presentations of a slow hidden leak in the supply pipework — either the mains supply pipe from the street to the house, or the internal distribution pipework. The leak loses water pressure upstream of your taps without any visible signs at surface level. Our detailed guide to low water pressure causes and solutions covers the full range of pressure problems — this guide focuses specifically on the leak scenario.

How a Hidden Leak Causes Pressure Loss

A leak in a pressurised supply pipe — whether from a hairline crack in copper, a failed compression fitting, or a corroded joint — bleeds water continuously from the system before it reaches the outlets. In a small leak, the loss is slow enough that the pressure drop is gradual rather than sudden. The tap still runs, the shower still works — just not quite as well as it used to. Over months, as the leak point widens or additional minor leaks develop, the decline becomes more noticeable.

Meanwhile, the lost water is going somewhere: into the ground beside the supply pipe, into the building fabric, or through a void that eventually becomes damp. In many cases the damp evidence emerges long after the pressure symptom has been noticed and dismissed.

The Meter Test

The fastest way to confirm whether a leak is present in the supply system is the water meter test:

1. Turn off every tap, appliance, and water-using device in the property
2. Locate your water meter — usually in a small plastic box in the pavement outside your property, or near the boundary of your land
3. Note the current reading. Ideally, take a photo of the display
4. Wait 30–60 minutes without using any water in the property
5. Check the meter again. If it has moved — even slightly — water is leaving the supply system somewhere

A meter that continues to move with everything off confirms a live leak. The next step is locating it.

Other Signs a Leak May Be the Cause

Pressure decline from a supply pipe leak is rarely the only symptom. Look for these accompanying signs:

• Unexplained damp patches on walls, floors, or ceilings — particularly near known pipe routes
• Soft or spongy ground in the garden along the line from the street to the house
• Water bills that have increased without any change in usage
• Discolouration or rust staining from taps — indicating disturbed pipework or a nearby joint failure
• A hissing or running water sound inside walls when all fixtures are off

Supply Pipe vs Heating System Leak

It's worth distinguishing between a supply pipe leak (which will show on the water meter) and a heating system leak (which won't affect the water meter but will cause the boiler to lose pressure). If your boiler keeps dropping below 1 bar and needing repressurising, the loss is in the closed heating circuit — a different system entirely. Our guide to boiler pressure loss covers heating circuit leak diagnosis.

What Detection Involves

A supply pipe hidden leak is located using acoustic listening equipment, thermal imaging, or tracer gas depending on the pipe location and construction type. In most cases, our leak detection team can identify the precise location of a supply pipe leak without any excavation — allowing targeted, minimal-disruption repair rather than digging up the entire supply run.

Read our detailed guide on how plumbers find hidden leaks for a full explanation of each method. To book a detection survey, book online or call 02039514510.

Frequently Asked Questions

Could limescale in the pipes cause gradual pressure decline?

Yes — in Peterborough's hard water area, limescale accumulation inside old pipes gradually narrows the internal diameter, restricting flow over years. This tends to affect all outlets progressively and is more common in properties with original copper pipework from the 1960s or 70s. A leak and limescale can both be present simultaneously. A plumber can pressure-test sections of pipework to determine whether the restriction is internal narrowing or pressure loss from a leak.

Is a slow supply pipe leak urgent?

A slow leak that isn't causing visible damage may feel like a low priority, but it will worsen over time — both the pressure loss and the damage from the escaping water. Water escaping beside or beneath a supply pipe saturates surrounding ground and, if adjacent to the building, enters the building fabric. The earlier a leak is detected and repaired, the lower the total cost of repair and reinstatement.

What if the leak is in the supply pipe under the pavement?

The supply pipe from the street to your property boundary is Anglian Water's responsibility — they will investigate and repair it at no cost if notified. The section from the boundary to your house (the "communication pipe") is your responsibility. A detection survey will confirm which section is leaking. If the leak is confirmed on Anglian Water's side of the boundary, report it to them with the detection engineer's findings as evidence.

How much does supply pipe repair cost?

A supply pipe repair where the leak is precisely located typically costs £400–£900 for a straightforward repair in accessible ground — replacing a short section of pipe or re-making a failed fitting. If the supply pipe itself is old lead or corroded galvanised steel, replacement of the full run from boundary to house with modern MDPE plastic pipe is recommended alongside the repair, typically costing £700–£1,500 depending on distance and access.