The principal microbiological contaminants found in drinking water of the United States are bacteria, viruses, and pathogenic protozoa. Each is considered in a separate section of this chapter. Helminths are included along with the protozoa. Little information is available on mycoplasma, pathogenic yeast, and pathogenic fungi in drinking water. Microbiological contaminants, such as fungi and algae, do not seem to be important causes of waterborne disease, although they are sometimes associated with undesirable tastes and odors.