Spring (water)

Spring (water), natural flow of water from the ground at a single point within a restricted area; when a spring has no visible current, it is called a seep. Springs may emerge at different points on dry land or in the beds of streams, ponds, or lakes. Cold spring waters are usually of meteorological character, that is, rain that has soaked into the ground and emerged as a spring at some other point on a lower level. Hot spring waters may be of igneous origin, or they may represent surface waters heated by contact with underground uncooled igneous rock, as the hot springs and geysers at Yellowstone National Park. See Geyser.

Classified according to their modes of origin, there are gravity springs, or those not confined by impervious beds, and artesian springs, in which the water is under pressure because it is confined to a pervious bed or a fissure (see Artesian Well). Grouped according to the nature of the water-conducting passages, springs are of three types: (1) seepage, in which the water seeps out from sand and gravel; (2) tubular, or those formed by tubular passages in glacial drift or easily soluble rocks; and (3) fissure, in which the water issues along bedding, joints, faults, or cleavage planes. Pollution is likely where the water flows, for some distance, in an underground channel way of somewhat open character.

The composition of spring water varies with the character of the surrounding soil or rocks. Volume of flow of any given spring may vary with the season and amount of rainfall. Seepage springs often fail in periods of drought or little rainfall. Nevertheless, some springs have a fairly constant and even large volume of flow and may serve as sources of domestic or municipal water supply (see Water Supply and Waterworks). Some springs are also of medicinal value because of the dissolved mineral substances they contain (see Mineral Water; Water).