The correct answer for the supply of water per person in an urban area in India is option 'C', which is 135 litres per day.

There are several factors considered while determining the appropriate supply of water per person in an urban area. These factors include the water requirements for drinking, cooking, bathing, sanitation, and other domestic uses. It is essential to ensure an adequate supply of water to meet the basic needs of the population while also considering factors such as population density, climate, and availability of water resources.

In India, the per capita water requirement can vary depending on the state and region. The Ministry of Urban Development, Government of India, provides guidelines for urban water supply, which recommend a supply of 135 litres per capita per day (LPCD) for domestic use in urban areas.

Here is a breakdown of the factors considered in determining the supply of water per person in an urban area in India:

1. Domestic Needs:
- Drinking Water: The supply of safe and clean drinking water is crucial for maintaining good health. It is estimated that an average person consumes around 2-4 liters of water per day for drinking purposes.
- Cooking: Water is required for cooking food, and the quantity may vary depending on the cooking methods and the number of meals prepared.
- Bathing and Personal Hygiene: A certain amount of water is needed for bathing, washing hands, brushing teeth, and other personal hygiene practices.
- Sanitation: Water is necessary for flushing toilets and maintaining proper sanitation facilities.

2. Non-Domestic Needs:
- Commercial and Industrial Use: Urban areas have various commercial and industrial establishments that require water for their operations. However, this is not included in the per capita water requirement calculation.

3. Availability and Conservation:
- The availability of water resources in a particular region plays a significant role in determining the per capita water supply. Areas with limited water resources may have lower per capita supply compared to regions with abundant water sources.
- Water conservation measures, such as rainwater harvesting, water recycling, and efficient water management practices, are also important factors considered to ensure sustainable water supply.

It is worth mentioning that the per capita water requirement mentioned above is a guideline, and the actual supply can differ based on local conditions and policies. Additionally, it is crucial to promote water conservation practices and raise awareness about the efficient use of water resources to ensure a sustainable and equitable supply for all.