Rice is often grown in paddies — shallow puddles (typically 15cm depth) carefully controlled to ensure the appropriate water depth. Rice paddies sometimes serve a dual agricultural purpose by also producing edible fish or frogs, a useful source of protein. The farmers take advantage of the rice plant's tolerance to water: the water in the paddies prevents weeds from outgrowing the crop. Once the rice has established dominance of the field, the water can be drained in preparation for harvest. Paddies increase productivity, although rice can also be grown on dry land (including on terraced hillsides) with the help of chemical weed controls.
Whether it is grown in paddies or on dry land, rice requires a great amount of water compared to other food crops. Rice growing is a controversial practice in some areas, particularly in the United States and Australia, where rice farmers use 7% of the nation's water to generate just 0.02% of GDP. However, in nations that have a periodical rain season and typhoons, rice paddies serve to keep the water supply steady and prevent floods from reaching a dangerous level.