I've been told tap water then another said bottled water, then 50/50 bottled water with summer coolant ?
Give us a clue ?

 

Only reason I can think for coolant would be to stop it freezing in the reservoir, in which case you may as well use screen anti-freeze. but surely that would leave a sticky residue over the IC. Tap water could possibly leave tricky limescale depending on where you live which would be a job for cilit bang (Look what it does to a IC, good as new).

 

distilled water only

 

Next time you de-frost the fridge or freezer, collect the water and use that.
JohnD

 

As has been said, distilled water will do the trick

Good thing there's loads of it lying about in work