Public water supply – hard water:\r Why is hard water generally objectionable for municipal supply and domestic use, even when it is otherwise safe microbiologically?

Introduction / Context:
Hardness in water is primarily due to dissolved calcium and magnesium salts. While hardness is not a direct health hazard, it has operational and domestic drawbacks that make it undesirable in public water supplies unless within acceptable limits.

Given Data / Assumptions:

• “Hard water” refers to elevated Ca2+ and Mg2+ concentrations, expressed as mg/L as CaCO3.
• Microbiological safety is a separate issue from hardness.
• Turbidity is a physical parameter unrelated to hardness.

Concept / Approach:
The primary issues with hard water are: excessive soap consumption due to scum formation with calcium/magnesium, and scaling of pipes, heaters, and fixtures. These increase maintenance costs and reduce appliance efficiency.

Step-by-Step Reasoning:
Identify the definition and effects of hardness.Eliminate unrelated factors: turbidity, pathogens, taste/odour are not defining features of hardness.Conclude that the main objection is soap consumption and scaling.

Verification / Alternative check:
Standards and design texts note recommended hardness ranges for domestic supplies and discuss softening when hardness exceeds target levels to avoid scale and soap wastage.

Why Other Options Are Wrong:

• Turbidity depends on suspended solids, not dissolved hardness.
• Pathogens are microbiological contaminants, unrelated to hardness.
• Taste/odour issues are more associated with organics, algae, or chlorine, not simply hardness.

Common Pitfalls:

• Confusing hardness with turbidity or microbial contamination.
• Assuming hardness implies unsafe water; it is an aesthetic/operational concern.

Final Answer:
It consumes more soap and causes scaling in pipes and appliances