This part of IEC 62877 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 international standard lays down requirements of the composition@ purity and properties of water in the absence of specific recommendations from the manufacturer.