I guess it does happen,but I have never carried pills or other water treatment (including water from home) in my 65 yrs of treading the woods in VA,NC,TN,KY,WV,MT and ID and I have never gotten any sickness from drinking water in the woods. I will say that I am careful about which water I drink. I think the problem is way over blown. I sometimes carry water from home if no water is available where where I plan to tread. But be safe as you want to be. OH yes--- I have never seen a cow pie in the back country.