I assume that you are talking about another bike other than the Wing.The wing has a sealed battery and needs no water to be added to. As far as other lead acid batteries for bikes are concerned, I believe it depends on the type of water that you have in the system. In some locals they have a very high mineral content, or "hard water" which is bad for the battery. In other area like NYC you can use tap water without too much trouble. To be on the safe side I would use distilled water which you can get at any auto parts store like Auto Zone,etc.