Thanks Larry, excellent link. I agree with the essence of that forum thread. An installation is either a Pond or a Pool. It cannot be both because of the human use factor and the related health concerns. Natural Swimming Pools can be built to conform to state and local building codes, it is the Health Departments that are the toughest to deal with. As long a the CDC continues to publicly advocate chlorine as the only effective bacterial control, not much can be done. If irradiated food is safe for human consumption then why isn't irradiated water? Why, because the chemical industry would take one h-ll of a bottom line hit if suddenly all Pool owners quit using chemical treatments. These chemicals, incidentally, are recommended to be use in amounts that will only maintain the levels of harmful microbes below Federal guidelines. If they were used in sufficient strength to completely sterilize the water, it would then be toxic to humans. Commercial grade UV Sterilizers, like those accepted for use in irradiating food, WILL reduce microbial levels to far less than chemical use AND the resulting water is completely safe and non-toxic to humans. All you have to do is to go out and convince the bureaucratic Po-Bahs.