Among the many methods of rain water harvesting is the method called Tudum or Monga. This mechanism draws water from a Kohli tank for irrigation. A straight tunnel across the base of the bund is constructed using stones for a small tank or a bori. At the mouth of the tunnel a log is pitched and plastered with clay. When water is required it is removed.
 
For medium or large tank, a straight tunnel across the base of the bund is constructed. It is made of stones over which a stair like structure called monghad is built with an opening called dachcha on each side. This is blocked with a stone slab or a wooden log carefully plastered with clay.
 
Sometimes at the base of the tank a hollow tree trunk is placed to which another hollow tree trunk with holes at regular distances is placed vertically. Cogs are used to plug these holes, which can be removed to draw water. As the tree trunks rot quickly the system requires frequent repairs. The stringent forest laws also make it difficult to obtain wooden logs.
 
Each method is modified to suit the needs of that particular area. But it has become utmost important to use some kind of rain water harvesting method. Many of the ancient methods of conserving water are dying out due to growing urbanization. This has affected the ecology. Hence now it is becoming important to use the best suited method to save and store rain water. Each builder in Kochi, Trivandrum and other parts of Kerala are trying to make use of the abundant rain received by this area.