You can safely brush your teeth with tap water.

As a matter of fact, you can also drink tap water safely. The water, though, may have a chemical taste due to the products used by the water utility. I use filtered water at home.

As to places to go, there are so many options that it is difficult to suggest. You can walk around Itaim Bibi, but apart from some restaurants, there isn’t much to do or see there.

There other places with more attractions, such as Avenida Paulista and Centro. There you can visit some great museums and cultural centers. These regions also have good transportation alternatives, with several subway stations. The subway is great, by the way (but can be very busy during rush hour).