The biggest problem with pools is pool water. It smells like chlorine, feels like chlorine, and burns your eyes. Systems exist that purify the water using UV light, similar to a backpacking UV purifier. Why limit ourselves to a small UV unit that only partly purifies the water though?
Line the bottom of the pool with large UV lights like the ones used in tanning beds. That way, the pool will be completely purified and the swimmers will get a nice, even tan at the same time. Swim goggles with UV protection required.
In the interest of safety the lights will only turn on for ~10 minutes every hour (or whatever is safe, I have no idea) and they can be set to turn on and off on a schedule to keep the pool clean when it isn't in use.
Vastly improved over last year's Gamma ray pool.-- DIYMatt, Jun 11 2013 Water absorption spectrum http://www.lsbu.ac.uk/water/vibrat.htmlSecond-to-last graph [spidermother, Jun 12 2013] After listening to the microbiologists at work, I no longer trust UV in any sort of sterility applications. Of course it's possible they may be making me a bit paranoid on the subject, although I haven't seen any signs yet.
If anybody needs me, I'll be ETO sterilizing the cat.-- MechE, Jun 11 2013 More practically, I'm pretty sure that sufficient UV radiation to penetrate the full depth of the pool would be severely dangerous (possibly lethal to divers) to anyone who happened to be swimming to close to the source. For a six foot deep pool, you're looking at (as near as I can tell) about two orders of magnitude reduction from top to bottom. As a very rough estimate, you would end up with something very close to 8x the full intensity of the sun, except purely in very nasty UV (UV-C) right near the lights.
If you've got a diving end, it works out to something more like 800x.
(Any can correct my numbers. This is based on a disinfection dose of 8000 micro watts/cm^2, an attenuation of .01/cm, and a full sunlight intensity of 1W/cm^2)
It works for water treatment because they use relatively shallow pools, very intense lights, and don't put humans anywhere near it when the lights are on.-- MechE, Jun 12 2013 The light doesn't have to penetrate the full depth of the pool - it just needs to gradually sterilize water as it passes near the lights. Convection and pumping (for filtration) will cause adequate circulation.
That said, I suspect that the best wavelengths for sterilization are shorter than the best wavelengths for safe tanning.-- MaxwellBuchanan, Jun 12 2013 The nasty sterilising wavelengths are very strongly absorbed by water (link), and very bad for you.-- spidermother, Jun 12 2013 The really nasty ones are, but they aren't generally used because of the ozone production, which is bad to have anywhere humans are working. I think the ones that are generally actually used are in the ~250nm range, and aren't quite as strongly absorbed.-- MechE, Jun 12 2013 random, halfbakery