What are some ways to purify water?

Question

It needs to be purified because I'm doing a report on Mars and the question was how would you purify water on Mars. Your living in a habitat and it must be self-sustained. In other words, you can add things to it like plumbing and all but you can't keep adding things and it would have to be environment friendly. :)

Answer 1

You can boil the water, iodine tablets....why exactly do you need it purified? Camping? Class?

Answer 2

add potash alum to purify water the formula is K2SO4.Al2SO4.24H2O

Answer 3

get a good filter at walmart