This standard applies to water for use with vented lead-acid cells and batteries, i.e. water for preparation of electrolyte and for topping up cells or batteries. The purity of refilling water has to meet higher requirements compared to filling electrolyte, because the impurities in the operating electrolyte will be gradually increased by regular addition of water. This standard lays down requirements of the composition, purity and properties of water in the absence of specific recommendations from the manufacturer.