The distribution mains are designed to meet the water demand of a particular area. The design of the distribution mains is crucial to ensure that the water supply is adequate and reliable. In this regard, the following points explain the design of the distribution mains:

Maximum Hourly Demand on Maximum Day
The distribution mains are designed to meet the maximum hourly demand on the maximum day. The maximum hourly demand refers to the peak consumption of water during a particular hour of the day. The maximum day refers to the day of the year when the water demand is the highest. The distribution mains are designed to meet the peak demand to ensure that there is adequate water supply during the peak hours.

Factors Affecting Maximum Hourly Demand
The maximum hourly demand is affected by various factors, such as the population density, the type of land use, the climatic conditions, and the time of the day. For instance, in a residential area, the peak demand may occur early in the morning when people get ready for work or school. In an industrial area, the peak demand may occur during the day when the factories are in operation.

Design Criteria
The design of the distribution mains is based on various criteria, such as the pressure requirements, the flow rate, the pipe diameter, and the pipe material. The design criteria are determined based on the peak demand and the hydraulic characteristics of the distribution system.

Conclusion
In conclusion, the distribution mains are designed to meet the maximum hourly demand on the maximum day. The design of the distribution mains is crucial to ensure that the water supply is adequate and reliable. The design criteria are based on various factors, such as the pressure requirements, the flow rate, the pipe diameter, and the pipe material.

I think option C is correct