can be detected by laboratory tests only. Table 9-3 identifies some of the common impurities in water and summarizes their effect on water quality.

Water samples must be forwarded to a laboratory for complete mineral or bacteriological analysis.

The factors that affect and determine the quality of water, such as physical, chemical, biological, and radiological contamination, are discussed later in this chapter.

SOURCE RELIABILITY a water source. The information gathered during the water reconnaissance may indicate a source of sufficient supply only to have the source dry up during periods of no rainfall. Study the hydrological data to determine the variations that may be expected at the water source.

Geological formations influence the reliability of a groundwater source. The amount of water flowing and the rate of flow maybe controlled by geological layers. The amount of water within a water table may be limited by impervious formations, as shown in figure 9-4. Therefore, it is important that information on the The reliability of a water supply is one of characteristics and properties of the geological the most important factors in the selection of

Table 9-3. - Common Impurities in Water