When you drive through heavy rain, your brakes can get wet. What might occur if the brakes are used?

When driving in heavy rain or deep standing water, your brakes will get wet. Water in the brakes can cause the brakes to be weak, apply unevenly, or grab. This can cause lack of braking power, wheel lockups, pulling to one side or the other, and jackknife if you pull a trailer. [California Commercial Driver Handbook]