best cheap water filter?

so whats the cheapest most effective and possibly easiest water filter i can use?

For the res?

If so how bigs the res?

rain water?

10 gal. res

Afore you run out and buy one why not give these folks a chance to talk you out of needing one? Whut is in your water that makes it so toxic ect? Do it come from Chernobly..Three Mile Island..Teddy Kennedy's house for example? Just trying to cover all the bases here. Thanks.

Big Wheel

chernoble.. thats great. so not necessary unless im using shitty whater ha? anybody else?