Water-supply design for industrial townships: When estimating total water demand for an industrial township, what percentage share is generally assumed for combined industrial and commercial water demand (as a fraction of the total supply)?

Introduction / Context:
In municipal and industrial water-supply planning, engineers must break down the total demand into domestic, institutional, commercial, industrial, firefighting, and loss components. A typical planning task is to assign a reasonable percentage to the industrial and commercial portion when specific factory data are not yet available. Using standard ranges prevents under-designing transmission mains, reservoirs, and treatment facilities.

Given Data / Assumptions:

• Preliminary design for an industrial township with mixed commercial activity.
• No detailed water-use audit from individual industries is available.
• Use conventional benchmark percentages taught in water-supply engineering.

Concept / Approach:
Textbook practice and many state design manuals suggest a planning allowance for industrial plus commercial demand in the range of roughly one-fifth to one-quarter of the total system demand for industrial townships. This assumes domestic use remains important but is not the sole driver. The exact split is refined later with metered consumption and category-wise connections, but the preliminary sizing benefits from a robust envelope.

Step-by-Step Solution:

Verification / Alternative check:
If later surveys show heavier industrial loads (e.g., steel, textiles, or refineries), the percentage can be recalibrated. Conversely, in service-sector towns, the commercial/industrial fraction may be closer to 10–15%.

Why Other Options Are Wrong:

• 10% and 10–15%: more typical of non-industrial towns; risk underestimation for industrial townships.
• 15–20%: borderline low for explicitly industrial settings.
• 30–35%: high for preliminary sizing and can lead to costly oversizing without evidence.

Common Pitfalls:
Copying percentages from purely residential towns; double-counting losses within commercial/industrial categories; ignoring diurnal variation and peak factors which must be addressed separately.

Final Answer:
20 to 25%