While living in the Colorado mountains, my water source was from a short stream running from a spring. This filtered water was pumped into a 1,000-gallon tank in my basement. All surface water is subject to some contamination, but in all the years it was used it never gave me any problems. I finally had it tested, and the bacteria count was some 50 times what was allowed. After that test, I figured I was living on borrowed time and decided to do something about it. After some research and having used it on my hot tub, I decided on an ozone system. The advantage of ozone is there is no chemical added to the water. Ozone is just oxygen with an extra oxygen atom temporarily attached to the normal O2 molecule. This acts like a super oxidizer that kills any living particle it encounters in the water tank. This includes bacteria, viruses, and various spores, like Giardia. Ozone then reverts within a second or two to a normal oxygen molecule and bubbles out of the tank.