Stages of the Water Treatment Process

Water treatment is the process to reduce the concentration of contaminants and convert water for its desired end-use. Drinking water generally requires a more stringent process than bath or laundry water. It is an ecologically sound practice to ensure that returning water into the natural environment does not have an adverse result. The stages of water treatment are complex and include chemical, mechanical and physical processes.

1. The Pretreatment Stage – Screens are utilized to remove large debris such as rocks, sticks and other trash from the water. The growth of algae may be controlled by a chemical additive during this stage. Sand, grit and gravel is allowed to settle to the bottom and separated from the water.


2. The Coagulation Stage – During this stage small particles, such as silt and other microbes are eliminated. The water is mixed in a large tank with chemicals such as alum, which causes small particles to bind or coagulate.


3. The Flocculation Stage - Over time, these smaller particles will form larger units called floc. The floc will slowly begin to grow dense and settle to the bottom of the tank   


4. The Clarification Stage – Clarification, also known as sedimentation, transpires in a large container. The water flows very slowly, as sludge collects at the bottom of the container. The sludge is removed by pumping or scraping the container.


5. The Softening and Stabilization Stage – Certain minerals in water such as calcium and magnesium develop scale on pipes, tubs and washing machines. Water containing a lot of these minerals is considered to be hard and water with too little of these minerals is considered soft, which corrodes pipes. Minerals may be removed from hard water or added to soft water to create a balance.  


6. The Filtration Stage – During this process suspended particles that make water appear cloudy are removed. The water is filtered by passing through granular material composed of layers of coal, garnet, gravel, sand and other materials.  


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   The Disinfecting and Fluoride Stage – Chlorine is generally added to disinfect the water by destroying many organisms that may cause disease. Fluoride is fed into the water supply to reduce tooth decay at this stage.