What are the contaminants removed during water purification?
Public water treatment removes small particles and dirt, solids, germs (parasites, bacteria and viruses) and some dissolved chemicals, and kills remaining germs with a disinfectant. Treatment steps include coagulation, flocculation, sedimentation, filtration and disinfection. Reverse osmosis removes additional dissolved particles. What is removed depends on the treatment used.
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What contaminants are removed during water purification?
The US Centers for Disease Control and Prevention (CDC) describes the main steps at a treatment plant. Each step targets different contaminants.
| Step | What happens | What it removes |
|---|---|---|
| Coagulation | Chemicals such as salts, aluminum or iron bind small particles together | Dirt and other small particles |
| Flocculation | Gentle mixing forms larger, heavier particles called flocs | Prepares particles to settle out |
| Sedimentation | Heavier clumps (flocs) settle to the bottom | Solids |
| Filtration | Water passes through sand, gravel or charcoal with different pore sizes | Germs including parasites, bacteria and viruses, plus dissolved particles such as dust and chemicals |
| Disinfection | Chlorine, chloramine or chlorine dioxide is added | Remaining germs |
What do advanced steps add?
- Activated carbon filters: remove bad smells, according to CDC.
- Ultrafiltration: very small pores pass only water and small molecules such as salts.
- Reverse osmosis: removes additional particles and is often used for recycled or salt water.
- UV light and ozone: can disinfect at the plant but do not keep working in the pipes.
Why add disinfectant at the end?
A leftover (residual) disinfectant keeps killing germs living in the pipes between the plant and your tap, says CDC.
Does purification remove everything?
No. How much is removed depends on the contaminant and the treatment. We do not give percentage removal rates, because we found no official figure we could open. Utilities must meet federal safety standards, and CDC says households on private wells are responsible for their own water safety.
What about home filters?
CDC notes that not all tap water needs home filtering. If you are thinking about one, understand your options first; your local water quality report is a sensible starting point.
Purified vs distilled water
Bottled purified water may be treated in different ways, so check the label. Distilled water is made by boiling and condensing, which leaves most dissolved minerals behind.
People also ask
What are the steps of water purification?
CDC lists coagulation, flocculation, sedimentation, filtration and disinfection.
Does reverse osmosis remove more?
Yes. CDC says reverse osmosis removes additional particles and is often used for recycled or salt water.
Why is chlorine added at the end?
It kills remaining germs and leaves a residual that keeps working in the pipes.
Sources
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