Water main replacement

When the main is the problem

The tell is straightforward: poor flow everywhere, including the kitchen cold tap, which in most houses is fed directly from the incoming main.

What gets replaced, and who owns what

Broadly, the water company owns the main in the street and the communication pipe up to the boundary. The supply pipe from the boundary to the house is normally the property owner’s, including any part running under a shared drive.

That division matters because:

• Your share is the supply pipe, and that is what we replace.
• The water company may replace their section at the same time, and some contribute to lead replacement schemes – it is genuinely worth asking before you commit.
• Coordinating both gives a better result than replacing only your half, particularly where the communication pipe is also old and narrow.
• Shared supplies exist in older streets, where one pipe serves two or more properties. That complicates things and it is worth establishing early.

Contact your water supplier before starting. The answer about contributions and about their own section is free and it occasionally changes the plan.

Why old supply pipes underperform

1. Lead, still present in plenty of older property. Narrow, and a water quality consideration as well as a flow one.
2. Galvanised steel, which corrodes internally until the effective bore is a fraction of the nominal. The classic ‘it has got worse over thirty years’ cause.
3. Undersized from the start, frequently where a small-bore pipe was adequate for a house with one bathroom and is not for a house with three.
4. Old blue MDPE, some of which has known issues, and some of which is simply small.
5. Joints and repairs accumulated over decades, each adding resistance.
6. Partial collapse or damage from ground movement or other excavation.
7. Scaling, which in hard water reduces bore over long periods.

What the work involves

1. Measure and confirmFlow and pressure at the stopcock, and at the external stop tap if accessible, to establish where the restriction actually is.
2. Establish the routeFrom the boundary to the house, and what is over it – drive, lawn, patio, planting, other services.
3. Agree the methodOpen trench where the route allows, or moling and directional drilling where it does not. Moling is far less disruptive across a lawn or a drive and it is not possible everywhere.
4. Size the new pipeFor the property’s actual demand, with an eye on anything planned – an unvented cylinder, another bathroom.
5. Notify and coordinateWith the water supplier, and arrange their side where relevant.
6. Install in MDPEDucted where it passes under hardstanding, at the correct depth, with correct fittings and a new internal stopcock.
7. Connect, test and disinfectNew potable pipework is disinfected before being brought into use.
8. ReinstateGround made good. Agree at the outset what that means for a drive or a planted area.

Lead pipes specifically

If your supply pipe is lead, replacement is worth considering on water quality grounds as well as flow – see lead pipe replacement.

Two practical points:

• Water companies often have lead replacement schemes and may replace their communication pipe free or at reduced cost when you replace your supply pipe. Ask before starting.
• Replacing only part of a lead run can be worse than replacing none, because disturbing lead pipework can increase release in the short term. Coordinate so the whole run goes together where possible.

And a note for anyone planning an unvented cylinder on a marginal supply: the incoming main is the ceiling. Fitting a cylinder that the main cannot feed produces mains pressure at every outlet and not much of it. The supply upgrade comes first, or not at all – see unvented cylinders.