Yeast Extract Agar is a medium rich in nutrients that permits the recovery of a wide spectrum of bacteria, yeasts, and moulds. ISO 6222 recommends this medium for the plate count of microorganisms in all types of water, including for human consumption. Tryptone provides nitrogen, vitamins, minerals, and amino acids essential for growth. Yeast extract is the water-soluble portion of hydrolysed yeast and is a source of vitamins, particularly of the B-group. Bacteriological agar is the solidifying agent. It is recommended by ISO 6222 that this medium is used for the enumeration of culturable microorganisms in potable water at 36 ºC and 22 ºC.