Teslinhiker's post illustrates just how much circumstances can and should influence your choice of treatment method. I agree that on a long hike, particularly in the desert or during a warm/hot summer day, your consumption will be measured in gallons per day, not counting what you may consume during the evening to accomplish full rehydration.

In the desert and in any circumstance where water might be scarce, you would be prudent to carry the water (yup, all 16 pounds) with you from the beginning and then the quality of the water would not be an issue.

If all else fails, just slurp up the water from the natural source and restore your water balance. Whatever is in the water is not as bad as severe dehydration, which is deadly. I have done that a fair amount and have never regretted it.