Water filtration in China?

I'm going to China with my mother this summer for 3 weeks, and my mother informed me that I can't drink the tap water. We will be staying in hotels (4 stars mostly), but traveling both in urban and rural areas. So if there are any environmentally friendly frugal jet-setters reading this,

* Is that true that I can't drink the tap water?
* Should I just buy water everywhere?
* What about some sort of filtration/sterilization for tap water instead?