Question
Why do we boil water before drinking it? What happens to the germs when water is heated?
Solution — Step by Step
Tap water, river water, or even well water contains microorganisms — bacteria, viruses, and protozoa — that are invisible to the naked eye. These are called pathogens (disease-causing agents). Drinking water with these pathogens can cause diseases like cholera, typhoid, and diarrhoea.
When we heat water to 100°C, the high temperature destroys the proteins and cell structures inside microorganisms. They cannot survive this heat — they die. This process is called thermal disinfection.
We need to keep water at a rolling boil (not just warm) for at least 1 minute. At higher altitudes (like hill stations), where water boils at lower temperatures, boil for 3 minutes to be safe.
After boiling, let the water cool in the same covered vessel. Transfer it to a clean, covered container for storage. If we pour it into a dirty container, we undo all the work — contamination happens again.
The final answer: Boiling kills bacteria, viruses, and other pathogens by destroying them with heat, making the water safe to drink.
Why This Works
Microorganisms are living things — they are made of cells with proteins, membranes, and genetic material. High heat (100°C) breaks down these structures irreversibly. Think of it like cooking an egg: once the proteins in the egg white “set,” they can never go back to being liquid. The same happens to the proteins in bacteria.
Boiling is the most reliable home method because it doesn’t depend on any chemical, filter, or electricity — just fire and a vessel. This is why it has been used across cultures for centuries, long before we understood what germs actually were.
One thing to note: boiling does not remove dissolved chemicals like arsenic, fluoride, or heavy metals. It only kills biological contaminants. For chemical contamination, we need a different treatment.
Alternative Method
If boiling isn’t possible, here are other purification methods:
Filtration removes suspended impurities and some microorganisms. A candle filter or cloth filter clears mud and debris but doesn’t kill all viruses.
Chlorination — adding a small amount of chlorine (bleaching powder) — kills most bacteria and viruses. This is what municipal water supply systems do at large scale.
UV purification (like electric purifiers at home) uses ultraviolet light to damage the DNA of microorganisms, preventing them from reproducing. Fast and effective, but needs electricity.
For your Class 6 exam, remember this hierarchy: Boiling > Chlorination > Filtration in terms of effectiveness against germs. Filtration alone is not enough to kill pathogens.
Common Mistake
Many students write “boiling removes germs from water” — which is technically imprecise. Boiling kills germs; it doesn’t remove them. The dead microorganism bodies are still in the water (harmless, but still there). If your exam asks “what does boiling do to pathogens?”, write kills or destroys, not “removes” or “filters out.”
A second trap: students sometimes confuse purification (making water safe to drink) with distillation (making water chemically pure). Boiling purifies water from biological agents. Distillation — boiling and collecting the steam — removes both biological and chemical impurities, but we don’t do that at home for drinking water.