how is the system of water storage tanks used for irrigation.

Water storage tanks catch and store the run-off of smaller catchment areas. The water stored in such tanks can be used for  watering the plants ( irrigation) by taking water through outlet pipe. The water coming through pipe can be divided into smaller drains that can irrigate every small part of the field. Sometimes, the tanks are also equipped with pumps to efficiently take out and deliver the water to fields for irrigation.