It is a 20A fuse if that matters and it has happened 3 times now.
The likeliest reason is a short-circuit (like when a hot wire touches vehicle ground) or the mechanical overload. You should first locate the cause, eliminate it and then replace the fuse with the properly-rated one.
Short in the circuit. Short in the wiper motor. Disconnect the electrical connector to the wiper motor and see if the fuse blows when you turn on the wipers. If it blows with the motor disconnected, you've got a short somewhere in the harness. If it doesn't, then you've got a bad wiper motor.
