For municipal design, the average rate of sewage flow generated in a community is generally assumed to be how relative to the average rate of water supply?

Introduction / Context:
Estimating sewage flow from water supply is a first step in sizing sewers and treatment plants. Not all supplied water becomes wastewater due to losses and consumptive uses, so a fraction of supply is used for preliminary design when local data are lacking.

Given Data / Assumptions:

• Municipal context without unusually high infiltration/inflow.
• Average daily conditions (not peak hour).
• Typical domestic water uses include outdoor irrigation, leakage, and evaporation.

Concept / Approach:

Empirical practice assumes sewage ≈ 70–90% of water supply on an average day, reflecting consumptive losses. The exact factor depends on climate, metering accuracy, and industrial discharges, but the sewage rate is generally less than the water supply rate.

Step-by-Step Solution:

Verification / Alternative check:

Utility audits routinely find average return flows of 75–90% depending on season and outdoor usage. Codes sometimes tabulate default return fractions for planning.

Why Other Options Are Wrong:

(a) and (b) contradict observed losses. (d) confuses per-capita supply standards with return ratios. (e) is false because water use strongly drives sewage generation.

Common Pitfalls:

Ignoring infiltration/inflow during wet weather, which can temporarily increase sewer flows beyond return fractions; designing only on average rather than considering peaking factors.

Final Answer:

Less than the water supply rate (typically a fraction such as 0.7–0.9 of supply)