According to IS 1172:1963 (water supply standards in India), the recommended per capita water requirement for average domestic purposes is _____ litres per person per day (lpcd).

Introduction / Context:
Per capita water demand standards are used by planners to size sources, treatment plants, and distribution systems. IS 1172 is the primary Indian standard prescribing typical residential and institutional demands under normal conditions.

Given Data / Assumptions:

• Average domestic use under normal (non-scarcity) conditions.
• Standard Indian practice as per IS 1172:1963 (and widely cited figures thereafter).

Concept / Approach:
IS 1172 recommends a baseline of 135 lpcd for domestic purposes in urban settings, considering drinking, cooking, bathing, washing, flushing, etc. This benchmark serves as a planning norm (subject to local by-laws and service levels).

Step-by-Step Solution:

Verification / Alternative check:
Many state manuals and CPHEEO guidelines echo the 135 lpcd figure for residential planning.

Why Other Options Are Wrong:

• 50–105 lpcd are lower than the commonly cited IS 1172 norm for average urban domestic use.

Common Pitfalls:

• Confusing domestic lpcd with institutional or intermittent-supply adjustments.

Final Answer:
135 litres