Water Treatment Plants Explained

Learn about the processes that occurred before you turn your tap on for a drink in Concerning Reality's video.

Access to seemingly unlimited drinking water from your tap is all thanks to your local water treatment plant. Water treatment plants usually take water from a natural source like a river, dam or well and treat it so that it is safe for humans at a mass scale to drink.

The complicated process starts with something called coagulation and flocculation. This process removes the natural particles that are found in the original a water source.

Coagulants are added to the water that makes this debris stick together. A typical coagulant might be aluminum sulfites which has the opposite charge of the suspended solids, so when the charges are neutralized it allows them to stick together.

The coagulants are added as the water enters the treatment plant, The water is then moved to flocculation basins where they are mixed slowly to ensure the complete coagulation process occurs, the water is then pumped to a sedimentation basin.

Here, the water sits and the sediment settles to the bottom of the holding tanks. This sediment is cleaned out at regular intervals.

The water from in the tank is moved over weirs so that the cleanest water at the top flows out into the next sets of tanks for the next process. Filtration is up next.

The water is usually pretty clean by this stage but filtration helps remove the bacteria Most water treatment plants use a sand filter. A sand filter is a low-tech but highly efficient way of purifying water.

Water flows through varying coarseness of sand with particles being caught when they run out of room to pass through. Next up is an activate carbon filter; think of this a giant version of your Brita jug.

After filtration, the water is then disinfected. There are three main ways to do this, chlorine, ozone treatment, and ultraviolet treatment. These can be used individually or in combination.


Once the water is clean - then it's time to pump it out to be used by the catchment areas population. For more information about how that happens - check this video of Concerning Reality on how water towers work.