It seems there is some confusion here. There are dry suits that are designed for really bad weather (gore-tex). I have one (Musto), but they are really hot to wear on normal conditions. except in winter, on cold days. There are another kind, that is made of neoprene and are designed for really extreme conditions and work also as a life vest, giving you some hours on the cold water.
If you fall on the water with a gore-tex one, it would not be dry anymore, because the seals are not waterproof, I mean on the neck and on the legs, not to mention that it is by the head that most of the temperature escapes and those have not any protection there.