water sits in the shower and doesnt drain properly

A shower floor is a shallow funnel. The tiles are laid on a screed shaped to fall toward the waste, and if that shaping is wrong, water sits. Once the tiles are on, the shape is fixed.

Why it is more than cosmetic

• Standing water finds every weakness in the grout and keeps the substrate permanently damp.
• It leaves mineral deposits that stain and are difficult to remove.
• It is the ideal condition for mould at the grout lines.
• Water sitting against a hob or a screen track works its way into the junction over time.

What can and cannot be fixed cheaply

A small pooling area near the waste can sometimes be improved by regrinding the tile surface or adjusting the waste height, which is a compromise rather than a fix. Where the fall is genuinely wrong across the floor, the only correct repair is to remove the tiles and screed, reform the fall, re-waterproof and re-tile. Anything short of that is managing the symptom.

If the bathroom is recent, this is a defect rather than a preference. Fall to the waste is a construction requirement, not a matter of workmanship taste, which makes it a legitimate warranty claim within the statutory period.