If the water in the coolant system has the opportunity to evaporate, you may wish to consider using soft water to avoid mineral build up in the coolant passages.
By soft, I mean truly soft, like rainwater or reverse osmosis water, not "water softener" soft, which just substitutes one mineral for another.
A good auto parts store sometimes carries anti-corrosion ingredients to "refresh" your antifreeze. If you run a plain water system, that might also add a measure of protection from rust and galvanic attack.
Finest regards,
troy