I use distilled water..distilled water is mineral free...less chance of adding minerals to the solution to change the ability of the product...some water is high in Calcium ..so it can neutralize some chemicals..like wheel cleaners with a lite acid base...also minerals used in a mix of APC and water can cause a haze on plastic...for 50 cents a gallon at wal mart...I would use distilled water....I make pure dionized water(as good as distilled) for my salt water reef tanks..I have 200 gallons on hand at all times...
also hard mineral water has adverse effects on soaps..can make them less effective...thats why people put water softners in the house...soap will not work good with hard water
Al