The correlation between the absorbance at a fixed wave-length of a betaine dye in an organic solvent and the water content of the same solvent has been investigated. The betaine dyes investigated are 2,4,6-triphenyl- N-(3,5-diphenyl-4-hydroxyphenyl)pyiidinium betaine ( I), 1-methyl-8-hydroxyquinolinium betaine ( II), 1-methyl-6-hydroxyquinolinium betaine ( III) and 2-methyl-5-isoquinolinium betaine ( IV), and the organic solvents are ethanol, isopropanol, acetone, dioxan, acetonitrile and pyridine. The possibility of determining a trace amount of water in an organic solvent is demonstrated. The sensitivity of the method depends on solvent and dye but for example, 0.06 mg of water in 1 ml of acetonitrile can be detected with III with an ordinary spectrophotometer. The limitations of practical applications are discussed.