The water resources of the United States of America, like the water anywhere on the planet, are an integral part of the global hydrologic cycle. Precipitation originates as evaporation from land and the oceans. Soil moisture is used by plants, which return more moisture to the atmosphere. Water that does not evaporate or transpire or seep into aquifers runs off to form the nation’s streams and rivers. Snow stored in winter in the mountains provides water for rivers and deltas in the spring and summer. Storms bring extra moisture; droughts arise from protracted periods of low rainfall – all as part of our natural climate.