A WATER TRUCK OPERATOR WAS BACKING A CAT 773 WATER TRUCK UP A RAMP BUT AT 90 DEGREE TO THE RAMP WHEN HIS RT REAR WHEEL OVER RAN THE EXISTING BERM CAUSING THE TRUCK TO OVERTURN. THE OPERATOR RE CEIVED BRUISES TO HIS LEGS AND BACK AND A LACERATION TO HIS RT. LOWER LEG. THE OPERATOR WAS RELEASED TO RESTRICTED DUTY BUT RECOVERED. THE OPERATOR BEGAN MISSING WORK ON 5-20-02. THE OPERATOR