insoluble, activated carbon does not affect the pH value or chemical characteristics of water. One ounce of activated carbon per 1,000 gallons of water is usually adequate. However, dosages up to 1 pound per 1,000 gallons can be used, depending upon the kind and degree of impurities present. Use of activated carbon in much higher dosages for removal of chemical agents is discussed later in this chapter.

NOTE: Treatment with activated carbon should always be made ahead of, or part of, the coagulation process, so the activated carbon and the various impurities absorbed by it are removed.

Aeration treatment consists of adding oxygen by exposing the water to air. The process has a two-fold action. Volatile odor- producing materials are released to the atmosphere, and the action of the air upon readily oxidizable materials causes a precipitation of insoluble oxides and hydroxides. Removal of hydrogen sulfide is an example of the formal action, while removal of iron is an example of the latter action. The aeration of water to rid it of the taste and odor of decomposing vegetable matter generally involves both actions.

Copper sulfate controls tastes and odors caused by small living organisms. This treatment is most frequently used in lakes and reservoirs. The copper sulfate is applied by towing a porous sack containing copper sulfate crystals behind a boat or by spraying a copper sulfate solution over the surface of the water. The amount of copper sulfate you should use depends on the type and concentration of organisms present. Dosages must be controlled because amounts greater than 2.0 parts per million (ppm) kill fish in the water. The amount necessary to remove microorganisms has no detrimental effect on human beings. Copper sulfate treatment is rarely used in field water supply for several reasons.

1. The advantage to be derived from treating an entire lake or reservoir frequently does not warrant the expense of the treatment when the length of time the water source is to be used is taken into consideration.

2. The amount of copper sulfate used entails considerations of wildlife, medical effects, and total water chemistry which are beyond the water supply technician's area of operation.

3. Superchlorination and dechlorination with activated carbon are effective for short periods although they are expensive for extended operations,

Temperature must be considered in the treatment of water. Lowering the temperature of water suppresses odors and tastes and, therefore, increases its palatability. In the summer, the temperature of deep lakes and reservoirs decreases sharply from top to bottom. By shifting the depth of intake, it maybe possible to draw relatively cool water even during hot weather. Water should be drawn from the lower depths when possible. Cool water is more viscous than warm water and thus is more difficult to filter. Cool water is more difficult to coagulate and chlorinate effectively than warm water because of slower reactions. Water treatment rates