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National Science Foundation

Water is all around us—in the sky, on the ground, in the air—continually changing form. Water's unique chemical properties make it the only natural substance that can be found in all three states: liquid, solid (ice) and gas (steam). The continual movement of water around the globe is known as the hydrologic cycle. Several processes take place within this cycle, including evaporation, condensation, precipitation, runoff and collection. During the cycle, water will change form many times.

A Special Report The Chemistry of Water