Former Democrat Party MP Watchara Petthong said on Tuesday that the incident took place at 5pm, adding that the complex could get flooded even without rains.
He blamed the flooding on defective construction, and warned that such incidents would expose people to risk of electrocution.
This is not the first time such an incident has taken place inside the huge complex, built at a cost of THB12.2 billion baht.
Between September and October last year, rainwater had leaked into several areas of the building, including the Suriyan Hall where MPs convene their meetings, and the office of Parliament President Chuan Leekpai, he said.
The incident happened again on March 1 when a large tap-water pipe on the eighth floor of the complex broke, causing leakage that looked like a big waterfall in the rooms of advisory teams and the House of Representatives deputy secretary-general, he added
The leaked water cascaded down three elevator shafts from the eighth floor to the basement, forcing suspension of the elevator service.
Watchara claimed that there were a series of other similar incidents that have gone unreported due to cover-ups by Parliament’s permanent officials.