I use tap water with addition Savlon - disinfectant. Now it is few months in a tub, ran from time to time and there is no any funny smells or algae.
In my computer water cooling system I was using tap water with Zoflora (smells nice ).
Now since a cooling unit is a small fish tank it is just water. I have free heating in a aquarium from computer . Plants growing great, but after a time I had to add some anti algae treatment to stop them growing in a system.