Most of the surface water originates directly from precipitation in the form of rainfall or snow. Ground water from springs also contributes to the flow of most of the streams. The various surface water sources along with their characteristics are discussed below:
Natural lakes and ponds:
Lakes are inland depression that holds standing fresh water throughout the year eg-lake superior, Caspian Sea, etc. Ponds are small temporary or permanent shallow water bodies. Their water is much more accessible than ground water or glaciers and uniform in quality than water received from rivers and streams.
Artificial reservoir:
These are formed by constructing hydraulic structures (like dams) across river valleys. The deeper and narrower the valley is. The easier it is to construct the dam. The water quality is similar to that of natural lakes and ponds.
Rivers and streams:
Water that does not evaporate runs off the surface towards the sea in the forms of streams and rivers. Water from these sources is generally more variable in quality as well as less satisfactory than the water from lakes and impounded reservoirs. The quality of river water and that of streams depends on various factors like the character and area of the watershed, its geology and topography, seasonal variations and weather conditions disposal of sewage and industrial effluents.
Sea water:
Though oceans contain about 97% of the total water in the world, but the high concentration of salts in sea water (about 3.5%) makes it unfit for human consumption . the places where sea water is the only source available, potable water is obtained from sea water by carrying out desalting or demineralizing . for eg. In Persian Gulf and in ships on the high seas.
Characteristics of surface water:
The quality of surface water changes with climate and weather conditions. It also varies with regions. It contains lot of sand due to the streaming action of water which erodes rocky surface producing sand. It also contains oxygen, inorganic nutrients and various forms of life like algae, fungi, bacteria, small insects and fishes.