Phenolic compounds are a sort of common pollutants in water. Phenol index becomes an expedite indicator for the evaluation of the contamination level of water samples, in spite of the knowledge of the individual phenol and its derivatives are also important. In this work, an environmental friendly method for the determination of phenols, using a segmented flow system based on the conventional method's reactions without the liquid-liquid extraction step, was validated. Three linear dynamic ranges using C(6)H(5)OH: 1-10 microg l(-1), 10-200 microg l(-1) and 0.2-2.5 mg l(-1), with a coefficient of variation lower than 2%, were obtained. Several method's performance parameters were determined: limits of detection, limits of quantification, precision through duplicate analysis and trueness using the reference materials purchased from LGC Promochem, RTC no. QCI-043-2 Lot:P1. Measurement uncertainty was evaluated using an interlaboratory approach based on proficiency testing data. Relative combined uncertainty for phenols in water samples, u(c)(rel)(gamma(sample)), of 0.054 were obtained, in according to those imposed by the Portuguese Legislation: target u(c)(rel)(gamma(sample))=0.58 for 1 microg l(-1) of phenol (surface waters) and target u(c)(rel)(gamma(sample))=0.06 for 500 microg l(-1) of phenol (wastewaters). A high efficiency reduction and elimination of reagents and wastes, reduction of analysis time and exposition of the analyst were also obtained.