Rahat is a slightly different irrigation system than others. Before being able to explain how it works, it is necessary to consider what irrigation is. Irrigation is the science of getting water to the land or soil by artificial means. In other words, it does not rely on rain or water that is already running under the ground. The water is necessary to aid in crop growth. This is why water needs to be consistent when it comes to the crops.
To have water spread out over the fields, it was necessary to form some type of water collection system. In some cases a moat has been used to collect water that was then taken directly to the fields via buckets and placed over the crops. In other forms wells were used to keep water contained to draw on it.
The Rahat System of irrigation requires a large well in which a wheel is used. The wheel is turned by oxen, buffalo or cows to get the water out of the well and then spread out over the crops.
Modern day irrigation lays pipes in the ground so that the water is spread over crops when a valve is turned and the water is allowed to flow. In the Rahat System, the oxen were used to make the water flow into buckets that could then be dumped evenly over the crops.
It was primarily used in the subcontinent in places like Africa and the Middle East. It is still used by some tribes, but for the most part other modern techniques are used.