SINGAPORE - Water leakage was to blame for the platform screen door glitch which tripped up the Downtown Line on May 3.

According to operator SBS Transit on Thursday, water had damaged electrical components of one of the screen doors at Botanic Gardens station.

The leak was caused by natural groundwater seeping in from a space above the screen door - believed to be the tunnel ceiling. The leak has since been filled with a polyurethane chemical to prevent water from getting through.

The platform screen doors at the station were last checked in September 2016 as part of routine maintenance. None were found to be faulty and no water seepage was observed then, SBS Transit said.

But after this incident, all Downtown Line and North East Line platform screen doors, as well as their electrical wiring and components were inspected. Minor water seepage was found at two doors at the Downtown Line's King Albert Park station.

"However, their electrical components were not affected and we have since grouted the seepage," a company spokesman said. "We are working with the Land Transport Authority on the water seepage issue.

"We apologise to all affected commuters for the inconvenience."

Leaks in tunnels have been the root causes of several rail incidents, from short circuits that caused tunnel fires to a major breakdown on the North-South, East-West lines on July 7, 2015.