Test at two stages: a flood test of the waterproofing before screeding and tiling, and a flow test of the finished installation. Testing only after tiling means a leak can only be found by removing the floor.
Stage 1: Flood test (membrane stage)
- Block the outlet below the drain.
- Fill the shower area with water to a shallow depth, covering the membrane and the drain flange.
- Mark the water level.
- Leave for the period specified by the waterproofing system manufacturer.
- Check for level drop and inspect the ceiling below if accessible.
This is the single most valuable test — it verifies the membrane-to-flange bond before anything is covered up.
Stage 2: Flow test (finished installation)
- Run the shower at full flow, including the rain head if fitted.
- Watch for pooling at the far end of the floor.
- Check that water clears within a reasonable time after the shower stops.
- Check for gurgling, which indicates a venting or trap issue.
- Inspect for leaks at the drain and at the walls.
What good looks like
| Result | Interpretation |
|---|---|
| Water clears quickly, no pooling | Fall and flow rate are adequate |
| Small amount of surface water that clears | Normal for textured tile |
| Water pooling more than a few minutes | Insufficient fall, or drain capacity too low |
| Water reaching the doorway | Flow rate insufficient for the shower output |
| Gurgling | Venting or trap issue |
| Level drop in the flood test | Leak — must be found before covering |
Practical notes
- Photograph the flood test — useful evidence if a leak appears later.
- Test with the grate in place for the flow test, since the grate affects flow.
- A tile-insert grate should be tested with the insert fitted, as its flow path differs.
- Re-test after any subsequent work that disturbs the drain or surrounding tile.
Related: troubleshooting a leaking drain · slow drainage