Heavy rain and surface water can cause aquaplaning. This is when the tread of the tyres can’t disperse the wet quickly enough so the car ‘floats’ on a layer of water, taking control away from the driver.
As soon as you feel you’re losing control, don’t panic. Keep your driving inputs smooth and to a minimum. Don’t hit the brakes: this will cause you to skid uncontrollably. Don’t adjust the steering either: when the tyres grip tarmac again this will cause you to spear off uncontrollably, possibly in a direction you don’t want to go in. Keep the steering following the road and allow the car to slow down naturally by easing your foot off the accelerator.
If you can, avoid aquaplaning altogether by concentrating on the road ahead and seeing the danger in advance. Slowing down before you hit the standing water will give your tyres a better chance of dispersing it.