Household sewage ordinarily consists principally of human excrement, toilet paper, garbage, dish water, and other wash water from the various plumbing fixtures and floor drains.

Many kinds of bacteria, at times disease-producing ones, are contained in the discharges from the human body. Epidemics of typhoid fever, dysentery, diarrhea, cholera, and other water-borne diseases may result from the pollution of the water supply with sewage. Pollution is carried by water moving underground, as well as by water flowing on the surface. This is especially true in limestone regions, where underground channels and rock crevices permit water to flow for considerable distances with little filtering action. Sewage used for fertilizing or irrigating crops[2] may contaminate vegetables or the udders of cows and thus spread disease. Anthrax, cholera, and parasitic worms may be present in the surface drainage from fields and barn lots. It is wise to regard all sewage as dangerous and to dispose of it promptly in a sanitary manner, so that disease germs will not pollute the water supplies or be spread by flies, animals, or man.