There must be a sufficient reserve of water to be used for cultivation in the dry season or during the dry spell. Therefore, it is necessary to set aside a part of the land to dig a pond on the principle that there must be enough water for cultivation the whole year round. According to His Majesty the King’s calculation, to cultivate 1 rai (1,600 square meters) of land requires about 1,000 cubic meters of water. So, for growing 5 rai of rice and 5 rai of field crops or fruit trees (10 rai in all) there must be about 10,000 cubic meters of water per year.