This International Standard specifies a titrimetric method using ethylenediaminetetraacetic acid (EDTA) for the determination of the calcium content of ground waters, surface waters and drinking waters. It can also be used for municipal and industrial raw waters, provided they do not contain interfering amounts of heavy metals. The method is not applicable to sea waters and other similar waters with a high concentration of salts. It is applicable to waters with calcium contents ranging from 2 to 100 mg/I (0,05 to 2,5 mmol/l). For waters containing more calcium than 100 mg/l, a diluted sample shall be used.