218 CONSERVATION OF GROUND WATER 



diverted in order to utilize one or more of its chemical or 

 physical properties, it is quite likely that those properties will 

 be affected by the use. Commonly the effect is to render the 

 water less desirable for other users who want to take advantage 

 of the same property, but not necessarily for users concerned 

 with other properties of the water. 



The basic properties for which water is used nonconsump- 

 tively might be catalogued as chemical or solvent action, of 

 major importance in industrial processing, by which soluble 

 wastes are carried away from body tissues or from industrial 

 processes or from the soil zone; buoyant action by which solid 

 materials or immiscible liquids are floated or suspended, as 

 in the washing requirements of industry and the disposal of 

 solids in sewage, the floating of logs and ships and the carry- 

 ing of sediment in streams; release or acquisition of heat, 

 which is essential for both cooling and for heating systems; 

 and the energy it possesses by reason of its position, used for 

 hydroelectric power as well as for transporting wastes or other 

 materials to lower elevations. 



Water for public use, whether from municipal systems in 

 urban areas or domestic supplies in rural areas, is largely un- 

 consumed. The unconsumed water goes chiefly into sewage 

 although there may also be some return to ground water from 

 lawns and gardens. The public use generally results in only a 

 slight increase of mineral matter in solution, and the principal 

 contamination is by organic materials such as household and 

 industrial food-processing wastes. Of all the materials added 

 to water by use, these organic wastes may be the most serious 

 hazard to public health, but they are also the easiest to elimi- 

 nate. They constitute only a small proportion of the total 

 volume, for sewage is commonly more than 99 per cent water. 

 Natural processes of separation, filtration, dilution, oxidation, 

 and chemical reaction will restore the quality of the used 

 water in time. And to avoid risk, it is possible to achieve any 

 desired purity of the water in sewage by treatment: "primary" 

 to remove the gross solids by settling, "secondary" to oxidize 

 the remaining polluting materials, and "complete" by sand 



