The UV spectrophotometric determination of phenol and chlorophenols in mixtures was performed by using multivariate calibration with partial least-squares in drinking and surface waters. Absorbance and their first derivatives were evaluated for mixtures of phenol, 2-chloro-, 2,6-dichloro- and 2,3,6-trichlorophenol or phenol, 2-, 3- and 4-chlorophenol with satisfactory prediction of errors of results in the 10-100 mmol.l^-1 range for drinking and surface waters in the presence of 1.0 mol.l^-1 NaOH and * 1.0 mmol.l^-1 EDTA using a calibration set with 17 standard solutions (full statistic design) and 24 wavelengths. Humic acids interfere and their influence must be eliminated by previous addition into calibration solutions. Kalman filtering gives more accurate results for samples containing monochlorophenols and phenol with very similar absorption spectra.