Definition check in water-supply engineering: Per-capita water demand is calculated in litres on which time basis for each person?

Introduction / Context:
Per-capita demand (often noted as LPCD) is a foundational planning parameter for source sizing, treatment capacity, and distribution design in municipal water-supply engineering.

Given Data / Assumptions:

• Per-capita demand refers to average consumption attributed to one person.
• Used in feasibility studies, DPRs, and design standards.

Concept / Approach:
By definition, LPCD stands for litres per capita per day. It captures domestic and sometimes a proportion of non-domestic uses depending on the adopted standard, and it is averaged on a daily basis for planning and comparison across systems.

Step-by-Step Solution:
Recognize the unit acronym: LPCD.L = litres, P = per-capita, D = per day.Therefore, it is litres per person per day.

Verification / Alternative check:
Most national and international manuals, including urban design guidelines, define demand targets explicitly in LPCD terms (e.g., 135 LPCD for domestic consumption under typical Indian urban conditions with sewerage).

Why Other Options Are Wrong:

• Per month / per year: not standard; lacks the daily operational granularity used for design.
• None of these: incorrect because a standard definition exists.

Common Pitfalls:

• Confusing daily design demand with hourly peak factors; peak factors are applied to LPCD-based averages.

Final Answer:
per person per day