Effects of high pH on water distribution systems:\r A high pH value in water does not typically cause which of the following issues?

Introduction / Context:
Water pH significantly influences corrosion, scaling, and microbial stability in distribution networks. Higher pH values tend to make water less corrosive and more scale forming, while lower pH increases corrosivity. The question asks which problems are not produced by high pH water.

Given Data / Assumptions:

• “High pH” refers to water on the alkaline side (pH > 8).
• Metallic distribution mains may include cast iron, ductile iron, or steel.
• Typical dissolved mineral content supports carbonate equilibria.

Concept / Approach:
At higher pH, water is less aggressive; calcium carbonate tends to precipitate, forming protective scales (incrustation). This reduces corrosion rate and tuberculation (localized nodular corrosion). Conversely, low pH enhances corrosion and iron tuberculation. Sediment deposits can occur under a variety of pH conditions due to solids entering the system or formed by precipitation at high pH.

Step-by-Step Solution:
Identify phenomena promoted by high pH: scale formation and possible sedimentation due to precipitates.Identify phenomena inhibited by high pH: corrosion and iron tuberculation.Therefore, the effects that high pH does not produce are tuberculation and corrosion.

Verification / Alternative check:
Stability indices (e.g., Langelier Saturation Index) become positive at higher pH, indicating scale forming tendencies and reduced corrosivity, which aligns with the selected choice.

Why Other Options Are Wrong:

• Incrustation and sediment deposits are more likely in high pH water due to precipitation of carbonates and hydroxides.
• Corrosion and tuberculation are characteristic of more acidic, aggressive water, not high pH.

Common Pitfalls:

• Assuming any deposit equals corrosion. Scale deposits may actually reduce corrosion by forming a protective film.
• Ignoring alkalinity and calcium hardness, which interact with pH to determine scaling versus corrosivity.

Final Answer:
Both tuberculation and corrosion