PROTECTION OF WATER SOURCES FROM HOUSEHOLD WASTES Under most farm conditions a safe place for the disposal of wastes is in the upper 3-foot layer of soil, where the action of bacteria tends to render it harmless. Tile disposal fields, such as are used with septic tanks, and earth-pit privies accomplish this if the water table remains several feet below the surface and if the location is remote from water supplies. Cesspools and other types of pits do not ordinarily confine contamination to their immediate vicinity and are not recommended except for special conditions. Sewage or other wastes discharged into abandoned wells or other pits that reach to the water table or below it are almost certain to contaminate the ground water. It is generally poor practice, and often illegal, to discharge wastes into surface streams. Streams do not necessarily purify themselves in 50 feet, 100 feet, or some other stated distance, as is commonly believed. They do tend to purify themselves over long distances through the action of sunlight, aeration, and other factors but may not be safe for domestic use for many miles below the source of pollution. Clear, sparkling water is not always safe drinking water. Streams in agricultural communities are subject to many sources of pollution and they are likely to become more contaminated as they merge into larger streams. SEPTIC-TANK SYSTEMS Septic-tank systems, if installed and maintained properly, provide the most sanitary method of sewage disposal for farmhouses equipped with running water. Ground water or rock close to the surface, lack of sufficient fall for the sewage to flow by gravity, and too small an absorption area for the effluent limit the satisfactory operation of a septic tank. When these conditions exist, special advice should be sought from a competent local sanitary authority. Adverse soil conditions can be overcome if sufficient fall and space are available. The five essential parts (fig. 1) of a septic-tank system are (1) the house sewer; (2) the septic tank; (3) the effluent sewer; (4) the distribution box; and (5) the disposal field. In special cases a grease trap (see fig. 11, p. 19) is added. To facilitate inspection and repairs it is good practice to keep in the house a chart showing the location of the tank and other parts of the system. A septic tank does not necessarily purify the sewage, eliminate odor, or destroy all solid matter. Its purpose is to condition the sewage or domestic waste by bacterial action, so that it can be disposed of in a more satisfactory manner. [Illustration: Figure 1.--A septic-tank system.] OPERATION OF A SEPTIC-TANK SYSTEM