Potable vs non-potable water

Potable water is water treated to be safe to drink, cook and wash with; non-potable water is water not intended for drinking. In Dubai the most visible non-potable supply is TSE — treated sewage effluent (recycled water) — used for landscape irrigation and district-cooling make-up, alongside greywater reuse; it's treated, but not to drinking standard. The two are deliberately kept as separate systems, and the single most important rule in plumbing is that they must never cross-connect: if non-potable water is ever siphoned or pushed back into the drinking supply (a backflow event) it's a genuine health hazard. That is the whole reason backflow preventers and vacuum breakers exist, and why non-potable irrigation pipework is often colour-coded (commonly lilac or purple) so nobody plumbs it into a tap. There's a domestic angle too: the water stored in your roof or underground tank is potable only as clean as the tank — sediment, biofilm or ingress can quietly make drinkable water non-potable in practice, which is why periodic cleaning by Al Ghubaiba's water-supply team matters. See also greywater.