Potable water chemistry — acceptable pH for drinking: Select the pH value that best represents neutral, acceptable drinking water quality within typical guideline ranges.

Introduction / Context:
pH is a master variable controlling corrosion, scaling, and disinfectant efficacy. Drinking-water guidelines typically recommend a range that avoids sour or bitter taste, pipe corrosion, and deposition while maintaining disinfection effectiveness.

Given Data / Assumptions:

• Typical guideline range for distributed water is approximately 6.5 to 8.5.
• Neutral pH is 7 at 25°C.
• No special process constraints are specified.

Concept / Approach:
Within the listed options, pH 7 is neutral and squarely within acceptable ranges. Extremely high or low pH values cause taste/corrosion issues and may violate standards even if not directly toxic.

Step-by-Step Solution:

Verification / Alternative check:
Operators often adjust pH using alkalinity control, lime, carbon dioxide, or corrosion inhibitors to keep within target ranges.

Why Other Options Are Wrong:
pH 5 is acidic; 9, 11, and 13 are progressively alkaline and outside typical consumer acceptability and corrosion control limits.

Common Pitfalls:
Confusing pH targets for coagulation optimization with distribution targets; ignoring temperature effects on pH measurement.

Final Answer:
7