Rice growers who have not started their main crop are being instructed to delay planting until next month, or see their crops shrivel in the fields as they fight over the increasingly scarce water supply.
Deputy government spokesman Sansern Kaewkamnerd said on Monday that farmers should postpone planting crops that require excessive amounts of water.
Farmers who did not follow the instruction would see their crops wither as the water supply dried up.
He asked for cooperation in conserving water not only from farmers but also households, which were asked to cease activities that consume a lot of water, such as operating home swimming pools.
"The government asks the governors of all provinces to persuade people to save water to protect their own living and to keep water in the reservoirs so that the Royal Irrigation Department can supply farmland and the Chao Phraya river basin as planned.
"I believe that if all Thai people cooperate, we can get through the water shortage crisis," Maj Gen Sansern said.
"The water shortage this year may be more severe than that of late last year. So everyone should cooperate and must not be careless," he said.
The Royal Irrigation Department reported that as of Monday medium and large reservoirs held 34.495 billion cubic metres of water, or 46% of their total capacity, but only 10.692 billion cubic metres could be used.
Agriculture and Cooperatives Minister Pitipong Phuengboon Na Ayudhaya said farmers who had not planted their main crop rice should postpone doing so until the end of July.
"The government does not want to see people fighting for water. The main crop of rice is grown on 3.44 million rai in irrigated areas... To prevent damage, farmers who have not yet planted their main crop are asked to delay it," Mr Pitipong said.
Lertviroj Kowattana, director-general of the Royal Irrigation Department, admitted on Monday that it was difficult to manage the water supply at this time.
Suchart Charoensri, irrigation director in Manorom district of Chai Nat province, said that unless those farmers who had not yet started their main crop delay planting, then both previously and freshly sown paddy fields would all be damaged. He supervises irrigation in the eastern side of the Chao Phraya River.
Ekasit Sakdeethanaporn, director of the Chao Phraya dam, said the flow of water into the dam was declining because farmers upstream were actively pumping water directly into their paddy fields. Under these circumstances the remaining water would be enough for only 36 days of consumption.
About 1.2 million rai of paddy fields had not been planted this main crop season yet, he said.