I wondered the same thing about the sun giving the pool the UV. However, I have read where the light source for the pool is a different wavelength, I believe UV-C, the sun puts out UV-A. Anyway, here is one of the websites I have been getting some of my information [ URL SNIPPED - PoolDoc. See post below.] I also went to DeltaUV's website and called them to get some information. I talked to a guy there that has been in the pool business for quite some time now, not just the selling side but plumbing, electrical all areas hands on. I told him I thought there weren't many people using the system due to the lack of information on the internet from other users and he informed me there was a little more than 10,000 residential pools in the US currently using the UV system. He kept me on the phone for a good 45 minutes and answered a plethora of questions about pool building, equipment and cleaning. It was a very informative conversation to say the least. Delta is a manufacturer of the UV system and he was able to point me to a few people who sell it in this area. He did mention that you must supplement the cleaning process with chlorine and went into some temperature thresholds for chlorine tablet use. I think it was something like 75-80 1 tablet, 80-85 2 and from there on up 3 a week. Anyway, I am a ways from deciding and will continue to research the idea.