The government plans to divert water from rivers which form natural boundaries with Thailand's neighbours into major dams in a long-term measure to battle drought.
Suphot Tovichakchaikul, chief of the Department of Water Resources (DWR), said Monday that aside from the country's local sources, water from the Moei River bordering Myanmar could possibly be diverted into the Bhumibol dam in the western province of Tak while water from the Mekong River could be piped to other major dams in the Northeast region.
However, neighbouring countries will need to be informed in advance of any water diversion.
Mr Suphot was speaking after a meeting of the National Water Board chaired by Prime Minister Prayut Chan-o-cha at Government House, also on Monday.
He said the water diversion project approved in principle at the meeting will be long-term in nature as it first requires an environmental impact assessment, a process which should take about a year to complete.
The government has been studying the feasibility of channeling water from border rivers for more than 10 years, he added.
According to Mr Suphot, the Bhumibol dam in Tak can take in more than four billion cubic metres of water as the drought has caused water levels to plunge.
In the future, if and when the diversion from the Mekong River is given the go-ahead, water will be drawn into sources in the Huai Luang River basin located in Udon Thani and Nong Khai.
Mr Suphot said construction of sluice gates to regulate water from the Mekong River is finished although pumping water into catchments areas in the Huai Luang River basin will take about a year.
The gates will also help keep out excess water from the Mekong River during the rainy season. About 300,000 rai of farmland in irrigated areas is expected to benefit from the water diversion.
However, bilateral agreements with Myanmar, Lao and Cambodia which share the Mekong River will need to be incorporated in the project, Mr Suphot said.
Meanwhile, the DWR released and updated water volumes in the four main dams of the Chao Phraya River basin. The combined water level in the Bhumibol, Sirikit, Kwai Noi Bamrung Dan and Pasak Jolasid dams stood at about 3.7 billion cu/m as of Monday.
The Bhumibol dam reservoir holds one billion cu/m of water, the Sirikit dam 1.8 billion cu/m, the Kwai Noi Bamrung Dan dam 333 million cu/m and the Pasak Jolasid dam 486 million cu/m.
The Metropolitan Waterworks Authority is releasing six million cu/m of water per day to support Bangkok and the surrounding provinces.
Of this amount, 49% is used by households, 32% by industries and the rest by government offices.
To address the current drought, Mr Suphot said the priority is to preserve water for residential use while maintaining the ecosystem.
Measures to systematically distribute water from dams and reservoirs are being unveiled in 548 districts across the country, having begun Monday and lasting until May. Artesian wells will also be dug to supply water to households and farmland.
Currently, about 59% of 928 districts nationwide are facing water shortages and Mr Suphot urged the public to use water sparingly.
Also Monday, Gen Prayut said the government will calculate the total amount of water which can be used nationwide to cope with the drought, which has already hit many areas.
Gen Prayut said the calculation is crucial for the water management plan, adding the public will also be kept updated on the water situation, which will help raise their awareness about water conservation.
In Chai Nat, the water level at the Chao Phraya dam dropped below crisis point, at 13.95 metres above sea level, as water continues to be discharged daily for maintaining the ecosystem and tap water.
In Sapphaya and Sankhaburi districts, many artesian wells are running dry due to constant pumping by farmers.
In nearby Phitsanulok, three districts — Wang Thong, Noen Maprang and Phrom Phiram — were declared as drought-disaster areas.
Provincial governor Chuchart Keelapaeng and local authorities inspected drought-hit areas in Bang Rakam district after several sections of the Yom River dried up, exposing the riverbed. Mr Chuchart, however, confirmed water was sufficient for consumption.
But the agricultural sector will face water shortages as poor rainfall in the previous year has forced dams to release less water to farms.