Provides practical advice on pretreatment, sampling, performance and evaluation of waters used in biotesting. Gives details on handling problems for biotesting which arise from the water sample and the test design suitability. Outlines practical experience regarding precautions to be taken by providing methods successful in proving they solve or get around some problems of biotesting waters. Particular emphasis is put on ecotoxicological testing with organisms. Some features outlined in this general guide are also applicable to biodegradation or bioaccumulation study as far as sampling and preparations are concerned. Poorly soluble substance preparation and testing beyond the water-solubility limit is also covered. Does not cover bacteriological water examination.