That board was very light JP slalom. I weighted it only after the incident (not before), but I think 95% of the water (or more) evaporated because:
1. Weight was corresponding to what jp quoted
2. It felt the same while sailing
3. It was sold afterwards, and a mate is sailing it today. Fourth season now, without delamination or other problems.
If you know what was your boards' weight before, than you'll know exactly how much water is in now.