Drinking water treatment is the process of making water safer to drink before it reaches homes, schools, and businesses. This reference covers the main steps in a water treatment plant, from source water to finished tap water. Students need this cheat sheet to understand how science and engineering help protect public health.
It also shows why clean-looking water can still need testing and treatment.
Key Facts
- A common drinking water treatment train is source water, screening, coagulation, flocculation, sedimentation, filtration, disinfection, storage, and distribution.
- Screening removes large objects such as leaves, sticks, trash, and debris before water enters the main treatment steps.
- Coagulation uses chemicals such as alum to make tiny particles clump together so they are easier to remove.
- Flocculation gently mixes water so small clumps combine into larger particles called floc.
- Sedimentation lets heavier floc settle to the bottom of a tank while clearer water moves on to filtration.
- Filtration removes many remaining particles by passing water through layers such as sand, gravel, or activated carbon.
- Disinfection kills or inactivates harmful microorganisms, and common disinfectants include chlorine, ozone, and ultraviolet light.
- Water quality is checked using tests such as turbidity, pH, chlorine residual, bacteria tests, and sometimes fluoride level.
Vocabulary
- Source water
- Water from a river, lake, reservoir, or groundwater supply before it is treated for drinking.
- Coagulation
- A treatment step in which chemicals help tiny particles stick together into larger clumps.
- Floc
- The larger clumps of dirt, organic matter, and other particles formed during coagulation and flocculation.
- Filtration
- The process of passing water through materials that trap or remove small particles.
- Disinfection
- The process of killing or inactivating harmful microorganisms in water.
- Turbidity
- A measure of how cloudy water is because of suspended particles.
Common Mistakes to Avoid
- Thinking clear water is always safe is wrong because bacteria, viruses, chemicals, or dissolved substances can be invisible.
- Skipping coagulation and flocculation in the treatment order is wrong because many tiny particles must clump together before they can settle or filter out well.
- Confusing filtration with disinfection is wrong because filtration removes many particles, while disinfection targets harmful microorganisms.
- Assuming more chlorine is always better is wrong because disinfectant levels must be high enough to protect water but still safe and acceptable to drink.
- Treating fluoridation as the same as disinfection is wrong because fluoride is added to help protect teeth, not to kill germs.
Practice Questions
- 1 A treatment plant has 5,000 liters of water and removes 80% of the suspended particles during sedimentation and filtration. How many liters' worth of particle load remains, using the original load as 5,000 units?
- 2 A water sample has turbidity of 12 NTU before filtration and 2 NTU after filtration. By how many NTU did the turbidity decrease?
- 3 Put these steps in the correct order: disinfection, source water, filtration, coagulation, sedimentation.
- 4 Explain why a treatment plant usually uses both filtration and disinfection instead of choosing only one of those steps.