A nutrient material prepared for the growth of microorganisms in a laboratory is called culture medium (plural: media). The microbes that grow and multiply in or on a culture medium are referred to as a culture. The medium must contain the right nutrients for the particular microorganism we want to grow. It should also contain sufficient moisture, oxygen, and a properly adjusted pH. The medium must initially be sterile, so that the culture will contain only the microorganisms we add to the medium. The growing culture should be incubated at the proper temperature. Culture media are used for the isolation and identification of bacteria that are of interest in such areas as food, water, and clinical microbiology. A wide variety of media are available for the growth of microorganisms. The preparation of culture media is a critical aspect of water quality testing. Commercially available dehydrated media are used and require weighing and dissolving of the powder in laboratory pure water.