Water resources include sources of fresh water that can be used for agricultural, industrial, household, recreational and environmental purposes. While the majority of water on Earth is salt water found in oceans, only 3% is fresh water, with over two thirds of fresh water frozen in glaciers and polar ice caps. The main natural sources of water are rainwater, oceans, rivers, lakes, streams, ponds and springs, while man-made sources include dams, wells, canals and other structures that access fresh water supplies.