Earth is called as blue planet because 71 percent of the earth’s surface is covered with water. The bottled water that is consumed today might possibly be the same water that once trickled down the back of a wooly mammoth. The earth is closed system, means that very little matter including water, ever leaves or enter the atmosphere. The earth has an abundance of water, but unfortunately only a small percentage is even usable by humans. The 99 percent is in the oceans, soils and icecaps. Remaining of 1 percent of water is useful for drink. Humans can use ground and surface water. Most of the water used by humans comes from rivers.
Water plays many different roles on the earth. Some at the poles in ice caps and some is in the snow and graciers at the top of high mountains. Some is in lakes, streams and some is in underground. But most of the water on earth is in the oceans. The sun energy causes water to evaporate from oceans and lakes into the atmosphere. Plants and animals also release water vapour into the atmosphere. When the atmosphere cools, water vapour condenses making clouds that might produces rain or snow. Water has been recycled in its different form as ice, liquid or vapour.
Surface waters include the oceans, rivers and lakes. Surface waters make up the majority of the water used for the supply and irrigation. Oceans which are the largest source of surface water. Since the oceans have high salinity hence the water is not useful as drinking water. Efforts have been made to remove the salt from the water. Rivers constitute the flowing surface waters. Water always flows from higher altitude to lower altitude. A river will eventually flow into an ocean. The land that is ungradient of any point on the river is known as the drainage basin or watershed. Sediment in the river can be helpful and harmful. Sediment when deposited on the banks and in the flood plain, makes excellent form lands. However, sediment can harm and even destroy dams, reservoirs and the life in the stream.
Water in the ground travels through pores in soil and rocks. The ability to travel through the rocks or soil is known as permeability. High permeability means that the water can travel quickly. Ground water can be found in aquifers. An aquifers is a body of water saturated sediment or rock in which water can be rapidly. In some areas, the bedrock has low permeability levels yet ground water can still travel in the aquifers. Ground water can travel through fractures in the rock or through areas that are weathered.