Hi JT,

I wont use this water for showers. There are a lots of diseases you can get from infected water besides legionaires. The best way is to clean out the cisterna so the next rainwater you catch won't be infected. Personally I always disinfect rainwater at my finca with a combination of clorine and UVC-light. I'm away for months sometimes and there will always be a bio-film on the rainwater after that amout of time.

Hope this helps,
Mark