This International Standard gives guidance for the determination of total carbon (TC), total inorganic carbon (TIC) and total organic carbon (TOC) in drinking water, ground water, surface water, sea water and waste water. It also defines terms and specifies interferences, reagents, and sample pretreatment for water samples. The method described in this International Standard applies to water samples containing organic carbon content ranging from 0,3 mg/l to 1000 mg/l. The lower limit concentration is only applicable in special cases, for example drinking water, measured by highly sensitive instruments. Higher concentrations may be determined after appropriate dilution. This International Standard does not deal with the instrument-dependent specifications. Purgeable organic substances, such as benzene, toluene, cyclohexane and chloroform, can also be determined using this method. Cyanide, cyanate and particles of elemental carbon (soot), when present in the sample, can be determined together with the organic carbon.