According to drinking-water guidelines and common standards, the acceptable pH range for public water supplies should be maintained approximately within:

Introduction / Context:
pH control is crucial for corrosion management, coagulation efficiency, taste, and disinfection stability. Most standards specify a desirable pH band to balance consumer acceptability and infrastructure protection.

Given Data / Assumptions:

• Treated potable water distribution conditions.
• Commonly cited desirable range in many national standards.
• Aim to minimize corrosion/scale while maintaining treatment efficacy.

Concept / Approach:
pH below about 6.5 can be corrosive to metals, while pH above ~8.5 can cause scaling and interference with certain treatment processes or taste. The 6.5–8.5 range is widely accepted as the desirable band for distribution systems, with utilities often targeting narrower control bands depending on alkalinity and corrosion indices.

Step-by-Step Solution:

Verification / Alternative check:
Cross-refer to national standards and WHO guidance indicating the same typical desirable range.

Why Other Options Are Wrong:
Lower ranges (4.5–6.5) are too acidic; 8.5–10.5 is excessively alkaline for most systems and can cause taste/scaling issues.

Common Pitfalls:
Assuming the range is a rigid legal limit everywhere; exact compliance bands may vary by jurisdiction, but 6.5–8.5 remains a common exam value.

Final Answer:
6.5 to 8.5