**Core Concept**
The question is testing the concept of water supply adequacy, which is a critical public health concern. Adequate water supply is essential for meeting the basic needs of urban populations, including drinking, cooking, and personal hygiene.

**Why the Correct Answer is Right**
The correct answer is 80 liters per capita per day (LPCD). This amount is considered sufficient to meet the needs of all urban domestic purposes, including drinking, cooking, and personal hygiene. The World Health Organization (WHO) recommends 80 LPCD as the minimum water supply requirement for urban areas. This amount is based on the average water requirement per person per day, which takes into account the water needed for drinking, cooking, washing, and other domestic purposes.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it is too low. A water supply of 20 LPCD would not be sufficient to meet the basic needs of urban populations.
**Option B:** This option is incorrect because it is too high. A water supply of 150 LPCD would be excessive for urban domestic purposes and would likely result in waste and inefficiency.
**Option C:** This option is incorrect because it is not a standard unit of measurement for water supply. While it may be a relevant unit in certain contexts, it is not the standard unit used by the WHO or other international health organizations.

**Clinical Pearl / High-Yield Fact**
The WHO recommends 80 LPCD as the minimum water supply requirement for urban areas. This amount is based on the average water requirement per person per day and is essential for meeting the basic needs of urban populations, including drinking, cooking, and personal hygiene.

**Correct Answer:** C. 80 LPCD.