Flood barriers will be installed at another 19 MRT stations in an ongoing move by the Land Transport Authority (LTA) to protect stations from flooding.
Vent shafts, glass panel gaps and other openings will be sealed at the stations.
The 19 stations - all on the Circle and North-East Lines - include Holland Village, Kent Ridge, Serangoon, Chinatown and Clarke Quay.
LTA has called a tender for the project, which will also involve flood-proofing a Circle Line facility at Bukit Brown and the North-East Line's Sengkang Depot. The tender will close next month.
This is the third batch of stations that will be outfitted with flood prevention systems. The LTA had previously awarded two tenders to set up flood barriers at 17 MRT stations for $7.8 million.
An LTA spokesman said flood barriers are needed at these 36 underground MRT stations as they do not meet the requirements in national water agency PUB's Code of Practice on surface water drainage.
She added that all current and future MRT projects will meet the requirements, including the Downtown Line and Thomson Line stations.
Under the specific section on the underground rapid transit system in the code, PUB states that it must be "stringently protected against flood risks".
In addition, the PUB said entrances at stations should be at least 1m above the adjacent ground level. If the height requirement is not met, PUB recommends installing watertight barriers at least 1m above flood or ground levels to protect underground stations and tunnels from flooding.
Such flood barriers are on standby at six stations in low-lying areas prone to flooding, including Tanjong Pagar, Orchard and Novena. The entrances at these stations have been modified so that the barriers, made up of watertight aluminium panels, can be stacked up to keep flood waters at bay.
It takes two people up to 15 minutes to install them.
Singapore has seen more flash floods over the past few years, caused by heavy and intense bouts of rainfall.
PUB chief executive Chew Men Leong had earlier said it "is not possible for us to eliminate flash floods".
Still, in a bid to minimise them, the PUB has stepped up its drainage maintenance from once to thrice a week. It is also planning to improve drainage at 36 more flood-prone locations.
Its measures include building the Stamford Detention Tank near the junction of Tyersall Avenue and Tyersall Road, as well as deepening and widening the Sungei Pandan Kechil canal.
These are on top of 176 ongoing drainage improvement projects islandwide, such as at major canals in Rochor and Alexandra.