Why do riad bathrooms sometimes smell?
The short answer
Dry water traps. Run the tap for ten seconds and the smell stops.
A water trap is a U-bend that holds a small reservoir of water between you and the sewer line. When the water evaporates — and in 45°C heat, a trap can dry out in days — sewer gas rises through the open pipe.
Riads predate modern plumbing by centuries. A proper system needs vent stacks — vertical pipes carrying sewer gas above the roofline. Installing one means drilling through walls sometimes sixty centimetres thick. Most renovators don't. Without vents, gases exit through the nearest opening: the drain in your bathroom floor.
Medina drainage connects multiple properties to shared channels. A blockage three doors away pushes gases back through your drains. Your riad owner can maintain their plumbing perfectly and still inherit the smell from a neighbour who doesn't.