Water Purification Systems?

Hi,
I live at Dancing Rabbit Ecovillage (another community featured in the recent "Off Grid" article series). My wife and I own and operate a straw bale Bed & Breakfast here in the village that is powered by solar and wind. http://milkweedmercantile.com/
We also have a rainwater collection system. Having a commercial kitchen which serves the public has sometimes been a challenge when it comes to the water system. The health inspector comes at random times to inspect things like the temperature of our refrigerators and of course tests the water. Our cistern water passes through a 5 micron sediment filter and then an ultra-violet light. Most of the time we pass but sometimes not. At these times, we "shock" the cistern with bleach, as per health department instructions.

Can you tell me what sorts of purification systems you've had success with? Thank you kindly for your time.

Sincerely, Kurt
kurtrabbit [at] yahoo [dot] com