An EMB-500 landed on a wet runway and because of surface contamination neither the normal antiskid nor emergency brakes could develop enough friction to prevent the aircraft from overrunning the runway's end.

Narrative

Normal ILS. Rain; and 14 KT crosswind. Touchdown was appropriate for a wet runway; on centerline; and on speed. I lowered the nose and applied brakes. The aircraft did not appear to slow at all. I then released and reapplied the brakes. Again; there appeared to be no slowing. I then reached for the EMER brake. I pulled it until the PARK BRAKE light illuminated. There appeared to be no slowing. At this point we were at the 1;000 FT marker; and the First Officer called the Tower to let them know that we were going off the runway. I released the brakes and diverted my attention to avoiding the hill that is in line with the end of the runway and steered toward the clearway to the left. Throughout the entire rollout; we appeared to have good directional control. We continued through a flooded field and slowly came to a stop. I shut down both engines; then the First Officer asked the passengers if they were ok. They advised us that they were uninjured. I kept BATT 1 on for lighting until some assistance arrived. Once we were deplaned with the assistance of the fire department; a Fireman closed the door and we were given a ride back to the FBO.