Organic compounds present in waters in ultratrace concentrations, especially in chlorinated waters, could influence public health after longer period of use. Most of these compounds can have mutagenic and cancerogenic effects. The main goal of the projec t is using of continuous liquid extraction for the risk assessement connected with the contaminated water consumption, mainly with water treated by chlorination. For the continuous liquid extraction of the organic compounds from water, an extraction colu mn with reciprocating plates will be tested. The extracts from the large amount of water will be tested by Ames test and the toxic compounds will be determined by chromatographic and spectroscopic techniques, especially GC-MS. The study will be performed on the model substances and on the real samples of drinking water from at least three localities (Praha, Brno, Č.Budějovice) as well.