The water was reportedly about 1m deep at one point.
41% of Singapore's average monthly rainfall in December fell in central Singapore over more than two hours.
The perpetrator is allegedly a middle-aged man who may have health or mental issues.
The police have yet to reveal the nationalities of the deceased.
The SCDF allegedly had to extricate the victims from the crumpled-up car.
The couple's driver was suspected of "dozing off" at the time of the accident.
A yoga expert advises against practising alone or trying new movements without the guidance of a qualified instructor.
The cyclists, both on mountain bikes, were unable to find their way back to the designated trails.
Some suggested the lorry skidded when braking rather than when changing lanes.
She may face up to 14 years in jail for her actions.