(a) This method describes a procedure for determining the odor (that is, the property that affects the sense of smell) of industrial water and industrial waste water. A suggested system for classifying odors is given as an appendix to the method. The method is applicable to the determination of odor intensity in terms of threshold odor number or odor intensity index (Note 1). Note 1. Odor intensity index is the number of times the concentration of the original samples is halved by addition of odor-free water to obtain the least definitely perceptible odor. (b) Industrial effluents may carry a myriad of compounds that contribute to odor difficulties and yet can be measured individually only with difficulty. Combinations of compounds can provide odor intensity or characteristics that cannot be anticipated from individual analyses. (c) Because of the variation in human sensitivity, high precision in determining odor intensity is not possible. There will not always be agreement on odor characteristics by various testers. Odor analysis provides the tool to measure variation in odor intensity at a given sampling point. The degree of variation may indicate the magnitude or importance of an odor problem. Determining the cause of the variation or the source of the objectionable characteristic may define the odor problem better than analysis for individual compounds.