There are various natural sources of water on the earth such as ponds, rivers, lakes, rain, glaciers, oceans, and wells.
- River Water – The river gets water from the melting of snow lying on the peaks of mountains or from the rain water which reaches them through many small and big drains. The various impurities present in river water are dissolved salts, dust, sand, some micro-organisms such as bacteria, and straw particles. The river water also contains effluents which are discharged into the river by the factories. The suspended solid particles are present in the river water are harmful to all the living organisms including man.
- Rain Water – The rain water is considered to be the purest form of natural water because it is usually free from any impurities. It is formed by the condensation of water vapor present in the cloud. When the rain water comes down to earth through the atmosphere then it dissolves in it the gases such as oxygen, carbon dioxide, and nitrogen which are present in the atmosphere. The rain water also brings down with it the smoke and dust particles as well as bacteria present in the atmosphere. The rain water falling over industrial areas also contain some acid in it. So, all these impurities are present in the rain water which reaches the earth.
- Sea Water – The water comes from all the rivers ultimately reaches the sea. All the mud and silt present in river water collects at that place where the river meets the sea. The dissolved impurities including salts present in the river water pass into sea water. In this way, rivers add more and more dissolved salts to the sea every day. Sea water contains about 3.6 percent by mass of dissolved salts.
- Well water – The rain water which falls on the earth seeps through the soil and goes down. Ultimately this rain water is stopped by several hard rocks and collects there and this underground water becomes available to us on digging the well and it is called well water. The well water contains some dissolved impurities which were present in the soil. In addition to this, well water may also contain suspended particles, bacteria, and other micro-organisms including eggs of insects and larvae as impurities.
- Lake water – The water in lakes comes from snow, groundwater seepage, melting ice, rain, and streams. Most of the lakes contain fresh water. There are millions of lakes all over the world and are found on every continent, deserts, and mountains.
- Ocean water – The water in the ocean get salt from different seas, and rivers so it contains saline water. It covers the area about 71 percent of the earth’s surface. There are about 97 percent of the world’s water resources in oceans and the remaining 3 percent of the world’s water is in the form of ice. Most of the oceans are linked by water and characterized by saline water.
- Glaciers – It is one of the main sources of fresh water for the entire world which comes into oceans and covers 71 percent of the earth’s surface.