PURIFICATION OF WATER SUPPLIES 169 



and other vegetable matter which, by its decay, might discolor 

 the water. 



Turbidity. - - Turbidity, due to the presence of suspended 

 particles of sand, clay, etc., in the water, may be greatly lessened 

 by storage for several days in a reservoir free from disturbing 

 currents, but in the case of very muddy supplies the water never 

 completely clears. 



On the farm the use of any of the various types of filter beds 

 is impracticable because of the expense and the skilled labor 

 required for their proper operation. Much may be accomplished, 

 however, by a careful application of the coagulation method. 



It has been found that a sediment that will go through the 

 finest filter may be removed by adding alum (aluminum sul- 

 phate), in the ratio of I grain of the chemical to each gallon of 

 water (or one pound to 7000 gallons). In practice, it will be 

 most convenient to calculate the volume of water in cubic feet 

 and allow I ounce of the chemical for each 60 cubic feet. This 

 treatment generally reduces the color in addition to removing the 

 turbidity. 



Odor and Taste. In most instances, the odor and taste in 

 surface waters are due to the presence of algous and other organ- 

 isms of minute size. Aeration, such as that effected by spraying 

 the water in the air for a few seconds, often accomplishes a con- 

 siderable reduction of the objectionable smell and taste, but 

 such treatment is seldom practicable on farms. The method 

 giving most effective relief is the so-called copper-sulphate treat- 

 ment used for removing algae, as described in a subsequent 

 paragraph. 



Iron. Iron, if present in objectionable amounts, is always 

 recognizable by its taste. It is found in many well waters and 

 frequently in those of springs, but, owing to the fact that it is 

 commonly precipitated on contact with the air, it is not usually 

 present in conspicuous amounts in surface waters. It may be 

 precipitated by the addition of lime, and removed from the water 

 by filtration. 



