Which one is not a water treatment?

Here's the solution to the question:

The question asks: "Which one is not a water treatment?"

Let's analyze each option:

• A. Prevention of infection: Water treatment processes, especially disinfection, are designed to kill harmful microorganisms and prevent infections. This is a primary goal and outcome of water treatment.
• B. Promotes good health: By making water safe to drink and free from contaminants, water treatment directly contributes to public health. This is a major benefit and purpose of water treatment.
• C. Prevention of waterborne diseases: This is essentially the same as preventing infection and is a fundamental objective of water treatment.
• D. Addition of aluminium and magnesium: While certain aluminum compounds (like aluminum sulfate) are used as coagulants in water treatment to remove suspended particles, the general addition of aluminum and magnesium as minerals is not a standard water treatment process. In fact, magnesium is a component of water hardness, which is often removed during treatment, not added. Water treatment focuses on removing impurities and disinfecting, not typically on adding these specific minerals.

Therefore, the addition of aluminum and magnesium is not considered a water treatment process itself. The other options describe the essential goals and benefits of water treatment.

The correct option is D).
$\boxed{\text{D) Addition of aluminium and magnesium}}$