This International Standard specifies a test method for determining the inhibitory effect of surface, ground and waste water on Pseudomonas putida. This method is not suitable for highly coloured test samples, or samples containing undissolved or volatile materials or substances which react with the nutrient solution, or which undergo changes during the test (for example by precipitation, or biochemical or photochemical degradation) and may give false results and/or impair the reproducibility. The method is also suitable for testing substances soluble in water (see annex A).