Beginner roller skating
In the Wet, Your Brake Is Whatever Keeps the Wheels Straight
Wet ground doesn't take away all your stopping power, it takes away one particular kind: anything that turns a wheel across your direction of travel. Dragging a foot behind you keeps the wheels roughly in line and still works. Putting a foot out sideways in front of you does the opposite, and skaters who've done it in the rain don't describe it kindly. Same skater, same skates, same street - the difference is the angle.
Wet ground does not take away all your stopping power. It takes away one particular kind, and knowing which kind is the whole difference: anything that turns a wheel across your direction of travel.
Dragging a foot behind you keeps the wheels roughly in line with where you are going, and it still works in the wet. Putting a foot out sideways in front of you does the opposite. Skaters grade the two very differently — the trailing foot is fine, the foot across the front is the one they warn you about in the strongest terms they have.
Same skater, same skates, same street. The only variable is the angle of the wheels.
So the wet-weather brake is whichever of your stops keeps things straight. Work out which of yours does that before it is raining, not while it is.
Keep going: this is one section of the full Roller Skating for Beginners guide — sizing, gear, stopping, and where to skate, in one page.