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## Where does the water in our taps come from? Tap water mainly comes from rivers or lakes or underground wells. The water from these sources is not pure. It may contain dissolved substances like gases from the air, nitrates and sulphates from the soil, bacteria, harmful germs, sand, grit, soil pa...

## Where does the water in our taps come from? Tap water mainly comes from rivers or lakes or underground wells. The water from these sources is not pure. It may contain dissolved substances like gases from the air, nitrates and sulphates from the soil, bacteria, harmful germs, sand, grit, soil particles, etc. Before the water reaches our taps, it is made fit for drinking by killing the harmful germs and by removing solid matter. This is done at waterworks. Every day, we use a lot of tap water in our homes. Most of the water we use in our homes is used for cleaning, washing, cooking and carrying away waste materials. Only a little water is used for drinking. ## Why is tap water dirty? We all are responsible for it. We mix all sorts of things with tap water - shampoos, soaps, toothpastes, detergents, wastes from food, human wastes, etc. This water containing wastes is called **sewage**. Sewage includes garbage, human wastes and water that has been used for cleaning, washing and bathing. **Sewage contains many dissolved and suspended impurities which we call as contaminants.** **The contaminants can be summed up as follows:** * **Organic impurities**: These include human wastes, animal wastes, food wastes, soaps, detergents, pesticides, etc. * **Inorganic impurities**: These include nitrates, sulphates, phosphates, metals, etc. * **Nutrients**: Like nitrogen and phosphorus * **Bacteria and other microorganisms**: These may cause diseases like typhoid, cholera, dysentery, etc. ## Sewage Sewage is also generated from factories, offices, hospitals, institutions, etc. Since sewage contains lots of germs and impurities, it is unfit for usage and is drained into the rivers or lakes. But, before reaching the river or the lake, the sewage has to be treated. This is done in Sewage Treatment Plants (STP) or Waste Water Treatment Plants (WWTP). ## Waste Water Treatment Waste water treatment refers to the process of removing contaminants from waste water. It includes physical, chemical and biological processes to remove physical, chemical and biological contaminants. The waste water generated from our homes or factories is taken into the ground by a set of pipes. It then flows to a waste water treatment plant. ## Screening The first step is to pass the waste water through bar screens to remove large objects like rags, wood pieces, stones, polythene bags, etc. It is necessary to remove these objects as they are harmful to the equipment used in water treatment. ## Grit and sand removal Water is then allowed to flow through grit and sand removal tanks to remove heavy objects from the water. This allows the grit, sand and other heavy objects to settle at the bottom of the tank.