Also doesn't standing water go putrid after a while???..
I forgot to say - I am sure water does but we haven't experienced that at all with our tanks or our well. I know the dams certainly can get stinky but I have never ever noticed particularly the tank water going off/stinky etc. In fact even on the hottest days we find the tank water is still quite cool in temperature.

Our well water does very rarely when it gets much further to the bottom but one good day of rain fixes that right up.

Nae x