Water from faucets, wells and other natural resources usually has dissolved minerals, salts and impurities. These minerals and salts fill the pores and form a layer on the plates, affecting the normal electro-chemical reaction that generates power in the battery. Presence of such chemical ions may drastically reduce the lifespan of the battery. Filtering tap water merely removes the suspended matter but not the dissolved minerals and non-ionic compounds. Advanced filters like ion-exchange or activated carbon filters remove most of the ionic and larger non-ionic compounds leaving smaller molecules in solution.
Distilled water contains no dissolved minerals, salts, organic and in-organic compounds that may harm the battery. Therefore battery manufacturers recommend distilled water for better performance and longer battery life.
Can RO water be used in battery?
Reverse osmosis is a different process from distillation. RO water is also considered mineral-free like distilled water. The process of reverse osmosis removes all kinds of unwanted impurities, salts and ions from water, making it fit for human consumption. Regular service and maintenance of RO keeps the hardness, pH and TDS under permissible limit.
Many inverter service centers use and suggest RO water for the battery top up, but they keep a check on TDS level, hardness and pH of water used to ensure that battery function is not hampered. But it is always recommended to use distilled water for your inverter batteries.