Cleaning your own water is a whole subject in itself, so take a look at the section on water purification. Not drinking water extends to not cleaning teeth with water too. In fact, you should get used to cleaning your teeth with toothpaste alone. It's a tad unpleasant to start, but you get used to it. Bottled water is, in general, safe, and each country has its common brand upon which you can rely.
People are often hard up, and filling bottles with Nile water can be a great way to make a few bob.
It's a fairly innocent venture, I'm sure, but you should never drink water from opened bottles. Whilst on the subject of water, I should point out a few extra things. Firstly, you should not take ice in your drinks. Freezing won't kill all the bugs in water. Never have ice.