An instruction for testing of the total content of non-volatile by steam phenols (resorcinol and naphthol alkyl derivatives) in water is given. The colorimetric method is based an the formation of red cobalt complexes specially with nitrosated resorcinol and naphthol series phenols when sodium nitrite and cobalt sulphate are added to the slightly acidic sample. Test Method I regards co-existence of phenolic compounds which can De subjected to mono- and dinitroso substitutions and subsequently give two types of cobalt complexes. Test Method II reports the test results as 2,5-dimethylresorcinol.