**Core Concept**
The World Health Organization (WHO) recommends a minimum daily per capita water supply to meet the basic needs of urban domestic purposes, considering factors like hygiene, sanitation, and drinking water.

**Why the Correct Answer is Right**
The WHO considers a daily per capita water supply of 110 liters to be sufficient for all urban domestic purposes, including drinking, cooking, personal hygiene, and sanitation. This guideline is essential for maintaining public health and preventing water-borne diseases. The 110-liter mark is often cited as the minimum threshold for adequate water supply in urban settings.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is not recognized by the WHO or any reputable health organization as a standard for urban domestic water supply.
**Option B:** This option is close to the recommended level but does not account for factors like water quality, storage, and distribution efficiency.
**Option C:** This option is significantly lower than the recommended level, which could lead to inadequate water supply for essential purposes.

**Clinical Pearl / High-Yield Fact**
A commonly cited guideline for urban water supply is the "110-liter per capita per day" standard, which helps prevent water-borne diseases and ensures public health.

**Correct Answer: C. 50 liters**