Let me throw in my 2 cents for what it is worth. Our lab is responsible for monitoring the health status of research animals. One common practice is to treat water with either chorine or acid to reduce microbiological contamination. Water is treated with chlorine to achieve 8-12 ppm of available chorine. At these levels the water does have bacterial static effects on intestinal organisms. Pseudomonas aruginosa is one indicator organism for which we monitor, being both an opportunistic pathogen as well a common fecal contaminate. Chorine levels are affected by light, organic materials (bedding, feces, etc.) and dissipation. Generally within 24 hrs, original chlorine levels of 8-12ppm are below 0.5ppm. When monitoring for Pseudomonas aruginosa levels (from feces), during the first 24 hrs, levels of the organism are below detectable levels, as the available chlorine levels are decreased (24hrs+), there is a rise in the detectable levels in Pseudomonas aeruginosa isolated from feces. It is general practice to change chlorinated water bottles every 2-3 days. Acidified water, reduced to a pH of around 3.0-4.0 is stable from both a chemical and bacterial static point of view for 5-7 days. The water for both mythologies is generally not palatable to humans. Pete