Can I drink tap water in Istanbul?

Officially the water is treated, but most locals don't drink it straight from the tap because of old pipes in buildings. People buy bottled water or use large water jugs at home.

I used tap water for brushing my teeth with no problem and drank bottled water. It's cheap and sold everywhere.

Buy the big 5-litre bottles from a supermarket if you're staying a few days. Much cheaper than small bottles from kiosks.