Main pipe can be designed as max daily (1.8 times of daily demand),distribution pipe can be designed as (max hourly of max daily (2.7 *max hourly of max daily). Distribution system is designed for 30 years, the demand reservoir for 50 years, the water treatment unit for 15 years and the pipe mains for 30 years.

**Answer:**

The pipe mains that carry water from the source to the reservoir are designed for the maximum daily draft. This means that the pipes are engineered to handle the highest amount of water that will be drawn from the system in a single day.

**Importance of Maximum Daily Draft:**

Designing the pipe mains for the maximum daily draft ensures that the system can handle the peak water demand without any issues. It guarantees that the pipes will have sufficient capacity to deliver water to the reservoir at a rate that meets the maximum daily demand.

**Reasoning behind the Choice:**

The maximum daily draft is chosen as the basis for design because it represents the highest water demand that the system is likely to experience on a regular basis. This demand can occur during periods of high water usage such as during the summer months or in densely populated areas. By designing for the maximum daily draft, the system will be able to satisfy the water needs of the users even during peak periods.

**Other Options:**

- Average Daily Draft: Designing for the average daily draft would result in an undersized pipe system that may not be able to meet the peak demand. This could lead to low water pressure and insufficient water supply during times of high usage.

- Maximum Hourly Draft of the Maximum Day: Designing for the maximum hourly draft of the maximum day would be an overly conservative approach. This would result in a pipe system that is much larger than necessary, leading to higher costs and unnecessary infrastructure.

- Maximum Weekly Draft: Designing for the maximum weekly draft does not take into account the daily variations in water demand. This approach would result in an inefficient system that is not able to meet the peak demand on a daily basis.

**Conclusion:**

In conclusion, the pipe mains carrying water from the source to the reservoir are designed for the maximum daily draft. This design approach ensures that the system can handle the peak water demand and provide sufficient water supply to the users during periods of high usage.

A