ABSTRACT
Water evaporates from oceans, soil, living things (transpiration), rivers and lakes. At some point this water vapour condenses to water or ice in the atmosphere and returns to the Earth's surface as precipitation. Some of this precipitation will infiltrate into the soils and rocks below the surface where it flows more slowly to river channels or sometimes directly to the oceans. The water remaining on the surface and in the upper layers of the soil will partly evaporate back to the atmosphere and partly run into lakes and rivers, many of which flow into the sea. There are four main stores of water. These are the world oceans, polar ice, terrestrial waters and atmospheric water. The oceans hold 93 per cent of the water, polar ice holds 2 per cent, the soils, lakes, rivers and groundwater hold 5 per cent and the atmosphere holds a thousandth of 1 per cent of water resources. The water held in glaciers and polar ice or deep within some rocks may be stored for several thousand years. The water held by plants may just be stored for a few hours.
