Which of the following methods does not make water fit for drinking?

Analyze the question: We need the method that does NOT make water fit (safe) for drinking.

Concept: Making water safe means removing or killing disease-causing organisms (pathogens) and harmful impurities.

Checking each option:

• A. Addition of chlorine: Chlorine kills bacteria and other microorganisms. This is the standard disinfection step in water treatment, so it makes water safe.
• B. Boiling: Heat kills germs, so boiled water is safe to drink. This is common in homes in Nigeria.
• C. Distillation: The water is vaporised and condensed, leaving behind dissolved salts, microbes and other impurities. It gives very pure water, so it makes water safe.
• D. Addition of alum: Alum (aluminium sulphate) is a coagulant. It makes suspended clay and dirt particles clump together and settle (sedimentation), so the water looks clearer. It does not kill germs and does not remove dissolved impurities or pathogens. Alum alone therefore does not make water fit for drinking. It is only one step in treatment and must be followed by filtration and disinfection (e.g. chlorination).

Answer: D. Addition of alum.

Tip: Remember the roles:

• Alum = clears (coagulation, settling)
• Filtration = removes solids
• Chlorine/boiling = kills germs

If a method only clears the water and does not kill germs, it is not enough to make water safe to drink.