Don't tap in to the water

A recent study in NSW by the Australian Government National Measurement Institute concludes an on-running dilemma for battery owners; should I be using purified water to top up my batteries or can I get away with normal tap water?

That depends on the quantity of impurities in the tap water. When a cell gases the water evaporates and escapes. Solids within the water cannot evaporate and fall to the bottom of the battery.

To replace the water that has evaporated more water must be added and with it comes a new batch of dissolved impurities that fall to the bottom of the battery when the water dissolves.

This ongoing process builds deposits of impurities in the bottom of the battery and the more dissolved impurities there are in the water, the faster the deposits increase and the battery's life shortens.

The prevalent dissolved solid in tap water is calcium or calcium carbonate, which neutralises the acid (resulting in lower battery voltages) and causes shorts circuits.

Total dissolved solids is the measurement of the quantity of a solid dissolved in water in parts per million.

The National Measurement Institute measured the TDS levels in tap water around Sydney. They found the highest reading at Padstow at 110 ppm and the lowest reading of 76 ppm at Homebush.

A reading of 110 ppm is considered of average quality in the US and Europe where battery companies will not warrant batteries unless the water used to fill has a purity level below 50 ppm. So undoubtedly the answer to the question, is tap water suitable for battery topping?, is an unequivocal; no.

The caveat is of course the cost, and the storage of purified water. Fortunately, there are now de-ionisers available from the more progressive battery dealers that will produce battery quality water for a mere $0.15 a litre.