If drinking (potable) water contains harmful bacteria, how does this contamination affect the suitability of the water for human use?

Introduction / Context:

Safe drinking water is essential for human health. Potable water should be free from harmful levels of chemicals and from disease causing microorganisms. When harmful bacteria contaminate drinking water, they can cause serious illnesses such as diarrhoea, typhoid, and cholera. This question asks how the presence of harmful bacteria affects the suitability of water that is otherwise considered potable, so learners must focus on safety rather than just appearance or minor physical changes.

Given Data / Assumptions:

• The water in question is intended to be potable, meaning safe for drinking.
• Harmful bacteria are present in the water, indicating microbiological contamination.
• Options mention effects such as making water unfit, smelly, coloured, turbid, or hard.
• We assume that harmful bacteria can cause water borne diseases even if they do not change the water's look or smell.

Concept / Approach:

Potable water must meet certain microbiological standards, including the absence of harmful pathogens. The presence of dangerous bacteria means that disease causing organisms are in the water, so it is no longer safe for human consumption. Even if the water appears clear, without smell or colour, it can still be unsafe if it contains pathogenic bacteria. Therefore, the most important effect is that the water becomes unfit and unsafe to drink. Changes like smell, colour, or turbidity may or may not occur and are not the main defining factor of potability. Hardness of water is related to dissolved minerals and is different from bacterial contamination.

Step-by-Step Solution:

Step 1: Recall that potable water must be safe for drinking and free from disease causing bacteria. Step 2: Recognise that harmful bacteria in water can cause illnesses such as diarrhoea, cholera, and typhoid. Step 3: Understand that the presence of harmful bacteria automatically means the water is not safe, regardless of changes in smell or appearance. Step 4: Compare the options and identify which one directly states that the water becomes unfit and unsafe to drink. Step 5: Select that option as the correct description of the effect of bacterial contamination.

Verification / Alternative check:

Guidelines for drinking water quality from health authorities emphasise that water should contain zero coliform bacteria and no detectable pathogens. Water tests measure bacterial counts to decide if a source is safe. These documents state that water containing harmful bacteria is unsafe for human consumption. They do not rely only on physical changes like smell or cloudiness to judge safety. This supports the idea that contamination makes water unfit to drink, even without visible signs.

Why Other Options Are Wrong:

Option B, that it always becomes strongly smelly only, is misleading because water can contain harmful bacteria without any noticeable smell. Option C, that it always becomes brightly coloured, is incorrect because many contaminated waters remain clear. Option D suggests that slight turbidity is acceptable, but any presence of harmful bacteria already makes the water unsafe, even if turbidity is minimal. Option E, hardness, is related to dissolved calcium and magnesium salts, not directly to bacterial contamination, so it does not describe the main effect of harmful bacteria.

Common Pitfalls:

People sometimes believe that water that looks clear and has no smell must be safe to drink, and may underestimate the risk posed by invisible microorganisms. Students may also think that any change in colour or smell is necessary for water to be unsafe. To avoid such misconceptions, learners should remember that microbiological tests, not just physical appearance, determine potability, and that any presence of harmful bacteria makes water unfit for drinking.

Final Answer:

Harmful bacteria in potable water make the water unfit and unsafe to drink.