There are a full range of options, attitudes and philosophies on this subject. It is not a black/white, either/or issue. The following thumbnail sketches are intended to go from one end of a continuum to the other, especially as related to wilderness hiking. With which philosophy do you most identify?
— Be suspicious of all water sources. Treat or disinfect all water supplies, even that carried to the trailhead (i.e., coming from known and dependable private or municipal water systems).
— Treat all backcountry water. Assume that all backcountry water is contaminated. Treat all water that does not come from a known and dependable private or municipal water supplies.
— Use double or triple treatment methods on most backcountry sources of water. For example, first filter the water and then use an ultraviolet or chemical treatment process.
— When in any doubt, treat. Treat all but the most pristine sources in backcountry wilderness areas. For example, assume that only springs that are well above any sources of contamination are safe to drink.
— Take a situational treatment approach. Decide to treat or not only after consideration of all relevant factors (e.g., water temperatures, watershed source, visual examination of site, level of human and livestock usage, opinions of local area managers, current strength of personal immune system).
— Travel in wilderness areas that are known for high quality water. Carry enough treated water to get one into the backcountry beyond most sources on contamination. Then drink freely. Put negatively; treat only water sources that are close to trailheads or close to obvious sources of pollution.
— Do not usually treat backcountry water: Use pristine sources when possible and condition your intestinal system to become immune to any backcountry contaminants when pristine sources are not available. Carry chemicals for treatment only in case of emergency when only obviously contaminated water is available.
— Avoid contaminated water. Use your knowledge and skill to select water from only pristine sources. Carefully plan your trip around such sources. Avoid all bad or questionable water sources. Do not treat the water from bad sources unless dying of thirst.
— If possible, totally avoid treated water in order to develop a high level of personal immunity. There is good reason to believe that most people suffer from gastrointestinal problems because their immunity has been compromised from drinking water that is too clean. For example, drinking chlorinated water could have this effect. While avoiding treated water, one should still be very selective in water sources. One should also expect to get some mild upsets until immunity has been fully developed.
— Other options?
These are most of the philosophies regarding the treatment of both frontcountry and backcountry water. What is your philosophy? What do you actually practice in the field? Do you need to rethink this whole subject?
To rethink your philosophy, consider reviewing a more detailed article on this subject To Treat or Not To Treat The Water? The sub-topics listed below are developed in this detailed article:
Working Definitions—Two Competing Approaches
Philosophies of Water Treatment: A Continuum
Reader Participation: Philosophy of Water Treatment
Arguments in Favor of Relaxed or No-Treatment Approaches
In Favor of Conservative, Disciplined, Hard-Line Treatment
Final Thoughts About Treatment
Additional Issues for Reflection