I want to make sure I have a sustainable water source for one household.

If I have a source of reasonably safe water like rain water or ground water, how can I purify this water to a level that I will know is safe to drink? 

Do I filter it, and how do I make these filters? 

Should I use distillation, or UV light?

Edit:
In my case I can collect a lot of rain water. I now collect this from the roof, but these roofs might be not the most suitable collectors (toxic materials?)