The Metropolitan Waterworks Authority (MWA) has urged households in the capital and its vicinity to reserve at least 60 litres of drinking water for the duration of the drought season until May next year.
The reduction of Chao Phraya River water usage is due to the problem of salt water intrusion, said Thanasak Watanathana, the MWA governor.
He said people living in the capital and nearby provinces, particularly Nonthaburi and Samut Prakan to which the MWA supplies tap water, should prepare to deal with possible water shortages during the drought season which lasts from now until May next year.
There will be less water to provide tap water to households living in Bangkok, Nonthaburi and Samut Prakan provinces, Mr Thanasak said.
To limit the effects of possible shortages, people should prepare containers to keep at least 60 litres of water for consumption per household, he said.
"The key message is that 60 litres can be enough drinking water for about one week. But it is not enough for other uses. Reserving water should be standard practice for households to deal with the drought next year," Mr Thanasak said.
According to the MWA, the Chao Phraya River will be at higher risk of salt water intrusion next year as water volumes released from dams will likely drop because of drought conditions. That will cause problems in tap water production.
However, Mr Thanasak assured that despite the reduced amount of water being released from dams, the MWA would not stop supplying tap water to 12 million users, including various corporate and state organisations, in the three provinces.
He said that the MWA has been concerned about the lower amount of water available for tap water production so it has reduced tap water pressure from 11pm-5am starting this month, curbing the water supply in that period.
If there is high intrusion of salt water, the MWA will cut Chao Phraya River water usage by 10%. Tap water production will then decrease from 5.4 million cubic metres per day to 5 million cu/m, he said.
Mr Thanasak said the possible water shortage would not be severe if everyone concerned takes action to save water.
According to the MWA, the average amount of water usage has currently been reduced to 219.5 litres per person per day from 223.5 litres per person per day.
From this month, the MWA will give refunds of 100-200 baht for each water user who reduced consumption by 10% during its water-saving campaign between August to September.
There are 428,819 users who will receive refunds worth a total of 43.7 million baht. The campaign saved 8.96 million cu/m of water.