Permanent secretary Chavalit Chookajorn said the present level of water in major reservoirs guarantees sufficient water for agriculture only in irrigated areas this planting season.
However, lower rainfall than normal to date meant many farms in non-irrigated areas were facing a water shortage.
The Royal Irrigation Department is advising rice growers in areas which rely on natural, small water supplies to postpone planting to prevent losses.
Mr Chavalit said the water stored in the major reservoirs nationwide totalled 35.14 billion cubic metres, only 47% of their combined capacity. This is more than last year by 1.18 billion cubic metres, he said. Large reservoirs have room for about 37 billion cubic metres of additional rainwater.
Bhumibol and Sirikit dams which control irrigation water supplies in the Central Plain, hold 7.41 billion cubic metres of water, about 32% of their combined capacity.