4 MASS. EXPERIMENT STATION BULLETIN 383 



According to their sources, waters are classified as rain water, surface 

 water, or ground water. (1) Rain water is really a "distilled water"; 

 that is, a water that has been vaporized and condensed. Distillation is 

 one of the best-known methods for purifying liquids. Thus, if properly 

 collected, rain water should be the purest type of water. 



(2) Surface waters, i. e., ponds, creeks, rivers, lakes, etc., vary greatly 

 in composition and are subject to impurities. From a sanitary standpoint 

 they are the most dangerous type of water to be used for drinking. Most 

 cities in America depend upon surface water for their supply. It is hardly 

 possible in a populous country to obtain any great amount of surface water 

 free from contamination with human wastes. It is for this reason that 

 the modern water-treatment plant has been constructed. Ry the use of 

 filtration and chlorination these plants render the water safe for human 

 consumption. 



In reality, streams are the natural sewers for the regions they drain. 

 It is inadvisable to use surface water as a source of supply without first 

 treating it to remove impurities. 



(3) Ground water is the type almost universally used as a source of 

 supply for rural homes. It is usually satisfactory as far as impurities go. 

 As water percolates through the soil certain impurities are reinoved by 

 the natural filtering properties of the soil. The soil can take care of a 

 large amount of impurities if not over-burdened, or if tliere are no cracks 

 or crevices. 



When water soaks into the soil it will finally come to rest upon an 

 impervious stratum. With its downward motion finally stopped, it then 

 spreads out in a horizontal plane, forming what is known as the ground 

 water tabic. This ground water table underlies practically all the earth's 

 surface. 



Ground water may be divided into tliree types depending upon the depth 

 at which it is tapped, (a) Spring water is ground water that comes out 

 on the surface because of the topography of the land. Spring water does 

 not necessarily diflfer in composition from other types of ground water. 

 It is of a high degree of purity and can be easily utilized if it has a good 

 flow. Spring water, liowever, can easily become contaminated unless 

 proper precautons are taken to protect it. The protection of springs 

 against contamination requires a careful study of each location. 



(b) Shallow well water is obtained from a source in which the ground 

 water table is very near the surface. It is perhaps the hardest type of 

 well water to protect from contamination, particularly in a dug well. 



(c) Deep well water is that usually obtained at a depth of 50 or more 

 feet. It is generally the purest of ground waters, and the easiest to protect 

 against contamination. Artesian wells are of this type. The water is 

 mostly obtained by suction pumping or by means of compressed air. 



Contamination of Water Supplies 



The greatest hazard to man in drinking water is found in a water con- 

 taminated with the discharges from the human body, i.e., feces, urine, and 

 sputum. There is really little danger from water containing the waste materials 

 from other animal life, for the reason that few of the diseases contracted 

 by the lower animals are transmissible to man. There is still less danger 

 from organic matter of plant origin. 



