The document describes a procedure to test if water is clean using a DBC reagent and selective enrichment medium. The procedure involves taking a 100ml water sample and adding the DBC powder, which contains substrates that react with enzymes from coliform bacteria. If the medium turns blue-green after incubation, it indicates the presence of coliforms, meaning the water is not clean. A fluorescent substrate also detects the enzyme from E. coli, distinguishing it from other coliforms. The procedure allows identification of microorganisms to investigate the presence of E. coli.