What is the minimum daily volume per dwelling unit?

• A. 300 gpd
• B. 350 gpd
• C. 400 gpd
• D. 450 gpd

Answer: (B)

The main idea here is using a sizing baseline for wastewater systems. Designers rely on a minimum daily volume per dwelling unit to ensure there’s enough flow to properly treat and dispose of wastewater under typical use. The figure of 350 gallons per day per dwelling unit is the commonly accepted starting point for this minimum. It reflects everyday household activities—toilets, showers, sinks, laundry—across a reasonable occupancy, while staying conservative enough to prevent undersizing.

Why this value fits best: it provides a practical, widely used default that keeps systems from being designed too small, which could lead to overloaded tanks or inadequate treatment. Less than that could underestimate actual usage, risking failures, while more than that would over-design and raise costs without a consistent need in typical scenarios.