The government is bracing for salt water intrusion into four major rivers, including the Chao Phraya, as low fresh water levels may have affected tap water production.
Authorities fear that a lack of fresh water will cause sea water to flow into inland rivers.
One vulnerable spot is Samlae station, which pumps raw water from a section of the Chao Phraya River in Pathum Thani's Muang district.
The station supplies water for tap water production for Bangkok and its outlying areas.
"We're working to prevent salt water from coming upstream to Samlae," Somkiat Prajamwong, secretary-general of the Office of the National Water Resources (ONWR), said.
He was referring to a prevention plan to be jointly carried out with the Royal Irrigation Department.
If salinity levels measured at the Rama III Bridge exceed permitted levels, irrigation officials will be asked to release more fresh water to dilute the sea water, Mr Somkiat said.
In case the Samlae facility encounters salinity beyond 0.25 grammes per litre, the ONWR will order water dilution.
"Then, we will need to replenish water into the Chao Phraya River by diverting water from the Mae Klong River," Mr Somkiat said.
He said up to 200,000 cubic metres of raw water a day from the Mae Klong is needed to maintain the quality of tap water.
"But any plans for water diversion must proceed with care," he said.
Officials are also required to check salinity levels of the Mae Klong, which is located to the west of the Chao Phraya and runs downstream to Ratchaburi, Samut Songkhram and the Gulf of Thailand.
A measuring device is installed at Klong Damnoen Saduak Canal in Ratchaburi's Damnoen Saduak district to inspect the river's water quality.
Similar equipment is also installed at Klong Chinda Canal in Nakhon Pathom's Sam Phran district and at riverside districts in Prachin Buri and Chachoengsao provinces to examine salinity levels in Tha Chin River and Bang Pakong River respectively.
Sea water intrusion will affect dozens of farm areas, ruining soil quality and threatening crops.
The Royal Irrigation Department has urged householders and farmers to use water economically as it plans to cut down water supplies until the end of April.
In the upper regions, authorities could only supply water for consumption, not farming, as water in 477 large- and medium-sized reservoirs this year are low, according to department chief Thongplew Kongjun.