Plumbing Contract Works · Question

Who is responsible for bathroom waterproofing around pipes and floor drains?

Short answer

The answer depends on the contract. Usually the waterproofing layer is a civil or specialist waterproofing scope, while the plumber places pipes and drain bodies and the junctions between them must be sealed by whoever the contract names. Because this interface is where leaks often start, the owner should have it written down, with one party accountable for the finished, tested result.

In more detail

A bathroom floor depends on several trades working in sequence. Plumbers fix the pipes and floor drains, civil or finishing teams form the slab and slope, a waterproofing applicator lays the membrane, and tilers finish the surface. Each trade can do its own part correctly and the bathroom can still leak, because the weak points sit at the joints between them.

The usual trouble spots are where pipes pass through the slab, around the edges of floor drains, and at the junction of floor and wall. If the plumber installs a pipe after the membrane is laid, or the applicator stops short of the drain body, water finds the gap.

So who is responsible? There is no single universal answer. In practice it follows the contract and the sequence of work:

If waterproofing is in the civil or interior contract, that contractor usually owns the membrane, but should be told where pipes and drains will be.
If it is in the plumbing contract, the plumber or a named specialist owns it.
The junctions around penetrations should be assigned explicitly to one party, with the sequence of work stated.

Gaps in scope become disputes

If the plumbing quotation says nothing about sealing around pipes and the civil quotation says nothing about drain edges, each party can say it was not theirs. Ask both to confirm in writing who covers the interface.

Ask for a water retention test of the finished floor, carried out and recorded before tiling, and again where the contract requires it. The method and duration follow the specification and applicable standards, set by the designer. Also check what warranty covers waterproofing and who honours it.

Key points

Leaks usually start at joints between trades, not in the membrane itself.
Responsibility follows the contract; the interface should be named in writing.
Sequence matters: pipes and drains should be fixed before the membrane is finished.
Ask for a recorded test of the floor before tiling covers the work.
Confirm warranty terms and who will attend to defects.

Who this applies to

Owners fitting out bathrooms or washrooms in new or renovated buildings.
Project managers coordinating plumbing, civil and finishing contractors.
Landlords and tenants dealing with leakage between floors.

Last reviewed 3 October 2026

This answer is general information, not advice on your particular case. Terms, eligibility, and requirements change, so check the current position with the relevant institution or authority.