The paper considers unfavorable consequences of the use of biotesting to define the conditions of effluent discharge into water objects. Evaluation of discharge hazard by the index "no toxicity" in the biological tests has been shown to allow both safe 100-1000-fold excesses of hygienic MAC in water; routine short-term experiments on biotest objects are not informative as to the substances that have carcinogenic and other long-term and specific effects; biotesting cannot replace the existing state system of sanitary standards and regulations which remain the basis of the population's health care in the field of water hygiene and sanitary protection of water reservoirs.
