The wet room failure nobody links to plumbing

You can spend good money on wet room conversions and still end up with a room that never quite feels dry. The culprit is often drainage gradients: not a blocked trap, not a leaky pipe, but a floor that never gives water a reliable route to the drain. It matters because the early signs look like “normal” splashing and condensation-until the grout darkens, the silicone fails, and the ceiling below starts to complain.

Most people blame the plumbing because that’s where the water is supposed to go. The uncomfortable truth is that plenty of wet-room failures happen before a pipe is even connected, when the slope, falls and levels are set. If those are wrong by a few millimetres in the wrong places, water will do what it always does: linger, creep and find an edge.

The failure you notice last

A wet room rarely fails with a dramatic gush. It fails with habits you build without realising. You start squeegeeing after every shower. You leave the extractor on longer. You keep a towel on the threshold because “it always pools there”.

When a wet room keeps asking you to manage water manually, it’s often telling you the floor doesn’t know where the drain is.

That’s why it gets mislabelled as poor ventilation, “bad tiles”, or an unreliable waste. In reality, the waste can be perfectly fine while the water is being asked to flow uphill, sideways, or across flat spots that act like tiny paddling pools.

What drainage gradients actually do

A wet room floor isn’t just tilted “towards the drain”. It needs a consistent set of falls that work with the position of the shower, the door line, and the rest of the room. Done well, you barely notice it; done badly, you feel it every morning.

The common gradient mistakes

• Flat zones near the perimeter where water sits after the shower finishes.
• Back-falls that push water towards the door or under cabinetry.
• A steep “ditch” right at the drain but not enough fall from the far side of the shower.
• Conflicting falls where two slopes meet and create a ridge that traps water.
• Drain placed for convenience, not for how the room will be used (e.g., outside the main spray zone).

None of these require a faulty pipe. They require a floor build-up that didn’t control levels with enough care, or a tray/former that wasn’t aligned, bedded, or cut as intended.

Why the plumbing still gets blamed

Wet rooms are quiet until they aren’t. Water can travel through pinholes in grout, around poorly supported tiles, or into corners where sealant is doing far more work than it should. When the damage appears, it shows up near pipework: a stain by the soil stack boxing, a damp patch near the vanity, a soggy ceiling under the bathroom.

That makes the narrative easy: “Something’s leaking.” A plumber gets called, traps get checked, pipes get pressure-tested. And if nothing obvious shows, everyone shrugs while the room keeps getting wetter.

A quick reality check

If the waste is coping (no gurgling, no slow drain, no sewer smells) but you still see standing water after a normal shower, you’re not chasing a blockage. You’re chasing geometry.

The tell-tale signs you can spot without lifting a tile

You don’t need specialist kit to see a fall problem. You need patience and a dry room.

1. Do a “cup test”: pour a small cup of water at different points in the shower area and watch where it goes. If it spreads out and stalls, the falls are inconsistent.
2. Watch the edges: water that tracks the wall line usually means the easiest route isn’t the drain.
3. Check the threshold: if water consistently reaches the doorway during a normal shower, the room either lacks sufficient fall away from it or the drain position isn’t doing the heavy lifting.
4. Look for repeat marks: dark grout lines and limescale arcs are maps of where water regularly sits.

If you have underfloor heating, these symptoms can be more pronounced. Heat speeds evaporation, which concentrates minerals and leaves staining that looks like “dirty grout” but is actually a record of pooling.

Where wet room conversions go wrong in practice

The floor build-up is treated like a normal bathroom

In a standard bathroom, minor level errors are usually cosmetic. In a wet room, they become functional. The build-up needs to be planned around:

• the drain type (centre, linear, wall drain),
• the substrate (timber vs concrete),
• the waterproofing system (tanked liquid vs sheet membrane),
• tile format (small mosaics forgive slope changes; large tiles don’t).

Large-format tiles are a particular trap. They look modern, but they resist compound falls, which tempts installers to flatten areas “for the look”. Water doesn’t care about the look.

The drain position is chosen too late

Move the drain 150mm and you can change the whole logic of the falls. In many wet room conversions, the drain ends up where the joists allow it, or where it’s easiest to connect-then the floor is forced to make that choice work. Sometimes it can. Sometimes it can’t, not without a lip, a ridge or a suspiciously flat corner.

What a good fix looks like (and what isn’t one)

Re-sealing, re-grouting, or swapping the waste can help if the room is otherwise draining correctly. But if the floor is wrong, surface fixes are often just buying time.

If water regularly sits on the finished surface, the long-term fix is usually to correct the falls, not to add more sealant.

A proper remedy typically involves at least one of these:

• re-forming the floor gradients with the correct former/screed,
• re-positioning the drain (sometimes with a different drain style),
• re-tanking the area as part of the rebuild,
• changing tile choice to suit the geometry.

It’s disruptive, but it’s also the point where the room stops needing “management” and starts behaving like it was designed to.

A simple decision guide

What you see	Likely cause	Best next step
Standing water after each shower	Poor falls / drainage gradients	Get falls checked before re-sealing
Water reaches the doorway	Back-fall or drain poorly located	Review drain position and floor levels
Damp below but no obvious leak	Water escaping via edges/voids	Inspect waterproofing + substrate

What to ask before you commit to a wet room conversion

You’re not being difficult; you’re being specific. Ask questions that force the plan to show itself.

• Where will the drain sit relative to the shower spray zone?
• How will the falls be formed, and what gradient range is being targeted?
• Which waterproofing system is used, and who guarantees it?
• What tile size is recommended for the proposed floor geometry?
• How will the threshold/door line be protected from back-fall?

A good installer will answer calmly and in detail, because they’ve already thought through the awkward corners. A vague answer is often a preview of a wet room that never quite dries.

FAQ:

• Can indicated drainage problems still be “plumbing” issues? Sometimes, but if the waste clears quickly and there’s no smell or backing-up, persistent pooling is more often a falls issue than a pipe issue.
• Do linear drains solve gradient problems automatically? No. They can make falls simpler (one main direction), but the floor still needs consistent gradients towards the channel with no flat spots.
• Is re-grouting ever enough? Only if the room drains correctly and the problem is cosmetic. If water sits on the surface, fresh grout usually masks the symptoms rather than fixing the cause.