naturally, water with less contaminates will leave less residue as it evaporates, and over the life of a -properly- maintained battery , it may be possible to have 100s of gallons of water evaporate, and be replaced.
But -very- few % of batteries really are properly maintained. so the difference is not worth the effort to provide de-ionized water, or even distilled water, if the tap water is clean enough to drink.
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