This is from the ISAF web site
here (ii) Camel backs
The issue of Camel backs (Drinking containers worn by the competitor), mentioned in the 1996 Olympic Regatta report dated October 1996, was discussed. Competitors will be able to carry drinking water on the boat. In view of the prohibition of weight jackets, camel backs will simply replace weight jackets.
Recommendation
For classes other than windsurfers, camel backs and similar devices must be prohibited by the Racing Rules Committee.
This was from the November 1996 Centerboard Boat Committee meeting minutes. The prohibition was placed in the 1997 rule book when they dropped the clothing weight limit from 15kg to 8kg.
The problem with water jackets is not while you are in the water. It's when you try to get
out of the water that there's a problem. Anybody that's gone for a swim in a leaky drysuit can attest to that.
