Mr Lertviroj also said the water in Kwae Noi Bamrung Daen dam in Phitsanulok province is sufficient for distribution for only one more month.
"The overall amount of water throughout the country has continued to drop because we have to drain it to maintain the ecological system and push back salty water. We have to stop distributing water for agriculture. This year's rain interval is expected between June and July," he said.
The Royal Irrigation Department chief said he had instructed a subcommittee for water management to carefully ration water.
He said an announcement will be issued to farmers to postpost the beginning of the annual rice planting season from early to late May because of the lengthy drought.