The per capita water demand refers to the amount of water required per person in a given area. It is an important parameter in water resource management and planning as it helps determine the overall water demand and the infrastructure required to meet that demand. In this case, the correct answer is option 'D', which includes domestic, commercial, public, fire, and industrial demand.

Below is a detailed explanation of why the correct answer is option 'D':

1. Domestic Water Demand:
- Domestic water demand includes the water required for household activities such as drinking, cooking, bathing, washing clothes, and sanitation. It is the basic water requirement for residential areas and is typically the largest component of per capita water demand.

2. Commercial Water Demand:
- Commercial water demand includes the water required for various commercial activities such as offices, hotels, restaurants, shops, and other commercial establishments. It includes water for purposes such as cleaning, irrigation, and cooling systems.

3. Public Water Demand:
- Public water demand includes the water required for public facilities and institutions such as schools, hospitals, government buildings, parks, and recreational areas. It includes water for drinking, sanitation, irrigation, and other public uses.

4. Fire Water Demand:
- Fire water demand refers to the water required for firefighting purposes. It includes the water needed for fire hydrants, sprinkler systems, and other firefighting equipment. This demand is crucial for ensuring public safety and firefighting capabilities.

5. Industrial Water Demand:
- Industrial water demand includes the water required for industrial processes and manufacturing activities. It varies depending on the type of industry and can involve significant amounts of water for cooling, cleaning, processing, and other industrial purposes.

By considering all these components, option 'D' (domestic, commercial, public, fire, and industrial demand) provides a comprehensive and inclusive assessment of the per capita water demand. This approach ensures that all major categories of water users are accounted for, allowing for better planning and management of water resources to meet the diverse needs of the population.