Unfortunately the use of adjectives in the English language is attended with so much latitude that the same term has often different meanings to different individuals. The character of adjectives describing natural or polluted waters has never been fixed by any national or international congress. Investigators and authors usually follow their own inclinations in descriptive terms, so that much confusion exists therefrom.

The term "pure" is generally applied in common language to all clear waters that show no sign of color nor turbidity. This common distinction of course is very apt to be misleading. Waters may be pure in the above sense and yet carry disease-producing germs which threaten health and even life.

The term "muddy" is applied to waters in which visible silt is suspended in quantities that make the water opaque. This condition is illustrated in the small streams after heavy rains in localities where the soil washes readily.

The term "bog" is applied to waters which are in contact with organic matter to such a degree and for such a length of time as to acquire a brown tint.

The term "putrid" is applied to all waters, usually stagnant, which acquire for any cause a bad smell.

From the sanitarian's point of view water is "polluted" when it contains any extraneous substance, derived especially from the surface, which tends to give it any property threatening to health. These pollutions may come from natural causes, that is, the decay of organic matter naturally in the soil or on its surface, or they may arise from excrementitious matter derived from dwellings, barns, poultry houses or pigpens.

The water is said to be "infected" particularly if it carries any pathogenic germ of a character suitable to reproduce the disease in the person consuming the water.

Finally, from the sanitary point of view a water is "pure" if it contains only the ordinary mineral substances which are extracted from the soil by the water and which are not of a harmful character, and when it is suitable for drinking and other domestic uses. In this sense the word "pure" has quite a distinct signification from the same word used from the chemical point of view.