Motorcycle riding in rain and floodwater
SPF's Riding Theory Booklet explains wet-road braking, skids, aquaplaning, and what to do if motorcycle floodwater crossing cannot be avoided.
Primary source: https://www.police.gov.sg/-/media/SPF/Advisories/RTTEN24.pdf
Wet roads and skids
The Riding Theory Booklet says a motorcycle's stopping distance on a wet road is twice the normal distance because the tyres have less friction with the road. Hard braking can lock the wheels and cause a skid or spin. If the motorcycle skids, steer in the direction of the skid and straighten the front wheel when traction returns. Riding while drenched and cold can also affect concentration (SPF, Riding Theory Booklet, p. 63). These are handbook safety guidance and estimates, not statutory stopping-distance rules.
Aquaplaning
Aquaplaning happens when water between the tyres and road reduces friction so the motorcycle glides; the booklet says the risk increases as speed increases and that good tyres cannot prevent it. Its countermeasure is to reduce speed using intermittent on-and-off braking to regain traction (SPF, Riding Theory Booklet, p. 64).
Floodwater
Avoid riding through floodwater if possible. If crossing cannot be avoided, the booklet advises selecting a lower gear, opening the throttle evenly to increase engine speed, and using half clutch to control speed. After crossing, do not speed up: apply the brakes intermittently at short intervals to dry them, and resume speed once braking effectiveness returns (SPF, Riding Theory Booklet, p. 64).
If visibility is poor, use the headlight and tail lamp. If it is so poor that the rider cannot see, stop at the side of the road and turn on hazard lights if fitted (SPF, Riding Theory Booklet, p. 64).
Coverage debt
The booklet does not specify a water-depth threshold at which a motorcycle can safely cross floodwater. It advises avoiding floodwater where possible but does not define a safe passability test.