No-Dig Underground Water Leak Detection in Nottingham

A supply pipe can leak for months without a damp patch, because the water drains down into the ground instead of up. On a water meter you pay for every litre of it, and the first sign is usually a bill that has doubled or tripled. Underground water leak detection finds the exact spot on the buried pipe so it can be fixed through one small hole.

The supply pipe runs from the boundary stop tap, usually in the pavement or at the edge of the drive, to the stop tap inside your house. Severn Trent says that pipe belongs to the homeowner, even where it crosses someone else’s land. So when the meter shows water going missing on your side, finding it is your job.

What we do on the first visit

The visit starts with the stop taps. With the internal stop tap closed and nothing running, the meter should stand still. If it moves, the loss is on the buried supply pipe. If it only moves with the internal tap open, the leak is inside the house, which is a different job.

Next comes the route. The supply pipe rarely runs in a straight line from the meter to the kitchen, so we trace it and find out what it is made of. Older Nottingham homes may still have lead or iron. Newer and replaced supplies are usually blue MDPE plastic. The material decides which method will work best.

Then a pressure test on the supply pipe confirms it is losing water, before any time is spent listening for the leak.

How the leak is pinpointed

Acoustic ground microphones

Water escaping under mains pressure makes a hiss. A ground microphone placed on the surface every metre or so along the route picks up where that noise is loudest. It works well on metal and lead pipes. Plastic pipe carries sound much less well, so a quiet leak on MDPE can be hard to hear.

Leak noise correlation

Two sensors go on fittings at either end of a section, such as the boundary stop tap and the internal stop tap. The correlator measures how long the leak noise takes to reach each sensor and works out where between them it started. This needs access to the pipe at both ends.

Tracer gas

When a leak is too quiet to hear, the pipe is drained and filled with a non-flammable mix of 5% hydrogen and 95% nitrogen. Hydrogen is the lightest gas there is, and it works its way up through soil, tarmac and paving joints. A detector swept over the surface finds where it comes out. This is the method for deep plastic pipes and leaks under hard standing.

Meter step tests

On longer or branched supplies, such as a pipe that also feeds a garden tap or an outbuilding, valves are closed one section at a time while the meter is watched. The section where the flow stops is the one with the leak.

Paying for it: insurance and Severn Trent

Two things can bring some of the money back.

Many buildings insurance policies include trace and access cover, which pays to find a leak and to open up and make good the area around it. Most do not pay to replace a worn-out pipe, and limits and excesses vary. Check the policy schedule before you book, and see what trace and access covers.

Separately, once a supply-pipe leak is repaired, Severn Trent can refund the water you lost as a one-off. It covers up to 12 months or two bills, based on actual meter readings. The repair has to be done first, so keep the invoice and the leak report together. How the Severn Trent leak allowance works goes through the claim step by step.