Hi Shanti,
We are planning on a foot-pumped water system in our van. I like both the simplicity and the control, which should lead to conserving precious water. My initial plan is to use 5 gallon jerry cans, and consider installing a larger water tank later.
As far as filtering, I suspect that the degree you are interested in would require a gravity-type filter such as the Brita or the Berkey, which is very popular with vanlifers.
Cheers,
Bob