While rain can make roadways dangerous, fault for an accident is often based on driver error, as the weather cannot be liable for a crash. If the conditions of the road are hazardous, every driver has a responsibility to others on the roadway to drive in a manner that would reasonably prevent a crash.
For example, a speeding driver who loses control of his or her vehicle and crashes into you would most likely be at fault for the collision due to his or her negligence, and therefore would be liable for your damages.
Some other factors that may play a role in a rain-related car crash include:
Tailgating
Aggressive driving
Failing to signal
Failing to use headlights
Another factor to consider is the condition of the vehicles involved in the crash. The driver of a vehicle with poorly-maintained tires could be the at-fault driver if loss of traction was a cause of the crash.