Explanation:
A canal is a man-made waterway that is used for various purposes such as transportation, irrigation, drainage, and hydroelectric power generation. In irrigation systems, canals are used to distribute water from a source to the agricultural fields. There are different types of canals based on their function, size, and location.

Main Canal:
A main canal is the primary waterway that is used to deliver water from the source to the distribution network. It is the largest canal in the system and usually runs in a straight line. The main canal is responsible for carrying the bulk of the water supply and delivering it to the secondary canals. It is designed to have a high flow rate and a large carrying capacity. The main canal is not supposed to do any irrigation as it is meant only to transport water to the distribution network.

Water Course:
A water course is a small canal that is used to deliver water to the fields. It is also called a field channel or a field drain. Water courses are designed to have a low flow rate and a small carrying capacity. They are used for localized irrigation and drainage purposes. Water courses are usually connected to the secondary canals or distributaries.

Major Distributary:
A major distributary is a branch canal that is derived from the main canal. It is designed to deliver water to a group of fields or a particular area. Major distributaries have a lower flow rate and carrying capacity than the main canal, but higher than the minor distributaries. They are responsible for distributing water to the minor distributaries or water courses.

Minor Distributary:
A minor distributary is a small branch canal that is derived from the major distributary. It is designed to deliver water to a single field or a small group of fields. Minor distributaries have the lowest flow rate and carrying capacity in the system. They are responsible for delivering water to the water courses or directly to the fields.

Conclusion:
In the given question, the canal which is not supposed to do any irrigation is the main canal. It is the primary waterway that transports water to the distribution network and is not designed to deliver water to the fields. The water courses, major distributaries, and minor distributaries are the canals that are responsible for delivering water to the fields for irrigation purposes.