Rain water treatment

I have a rainwater butt that I use to water all my bonsai - evergreen and coniferous. Because of the hot water it sometimes stinks. Does anyone have any ideas of safe water treatment. I did read up about a silver/copper disk to kill off bacteria and fungus. Any tips would be most welcomed.
Dan

Sorry folks...............hot water should read hot weather, although in these extreme temperatures it does warm up a little

There are absolutely no need for water treatment.