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Rain Water—Atmospheric influences.

Spring and Well Water—Mineral properties.

Rivers, Lakes—Vegetable and animal organisms.

But what can we consider good drinking water? Dr. Frankland, of England, has given the following as a minimum limit of mechanical and chemical impurities held in suspension or solution, to be considered bad or polluted liquid:

A. Every liquid which has not been submitted to precipitation, produced by a perfect repose in reservoirs of sufficient dimensions, during a period of at least six hours; or which, having been submitted to precipitation, contains in suspension more than one part by weight of dry organic matter in 100,000 parts of liquid; or which, not having been submitted to precipitation, contains in suspension more than three parts by weight of dry mineral matter, or one part by weight of dry organic matter in 100,000 parts of liquid.

B. Every liquid containing in solution more than two parts by weight of organic carbon, or three parts of organic nitrogen, in 100,000 parts of liquid.