If you're opposed to chem treatment (taste presumably?) and don't like the extra 13oz of a filter, look into a steripen. No taste, kills -well, neutralizes at least- everything (if used correctly and weighs in at less than 5 ounces (adventurer model).
As for the question, I'm going to echo the above two responses; if you have to ask it's best to treat (or at least have the option available).
Cogito ergo ambulo cum sacculo