Depends somewhat on the nature of the water coming out of the hose. If it is very hard (i.e. lot of minerals), I would suggest either using distilled or at least diluting the tap water with distilled. Some will say distilled is corrosive (which it is), but the coolant provides plenty of ions to deactivate the corrosiveness (sp?).

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Keep everything as simple as possible-but no simpler--Albert Einstein