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Water is the liquid of which seas, lakes, and rivers are composed, and which falls as rain and issues from springs. When pure, it is transparent, colorless (except as seen in large quantity, when it has a blue tint), tasteless, and inodorous. This is the Oxford dictionary's definition, similar to Webster's, having arisen from that of Samuel Johnson of 1755. Water's development into H2O came later.
Even early definitions recognized that water does not in nature begin by being pure; most closely approximating purity is rainwater. Man has always polluted water, even as he has turned it to his use. He pollutes it with his agricultural, industrial, and personal wastes, and he has always polluted it at a greater rate than he has purified it. The westward march of the American frontier was a march away from polluted to fresher, undammed waters, drained from untilled soils. The great
WATER. JAMA. 1965;191(12):1023. doi:10.1001/jama.1965.03080120057019