Like Hank says...

The CD has the option to declare a conventional "no water" day or a
"limited ballast" day, in which everyone flies at the same gross
weight. Which one he/she chooses will depend on a lot of things; the
reason for limiting water, and the impact on contest fairness.

The "limited ballast" idea gives you a bit more fairness in a single-
class contest like 18m nationals, where some gliders have motors, it's
a strong day, and people are really competing hard.

For reasons mentioned, "limited ballast" could well be less fair in a
mixed class regional if the class has widely different gliders in it.
So calling a "no water" day could be a better option.

These are tools. Use them wisely.

I don't think anyone is going to win an 18m national in a 15m glider
based on higher wingloading on "limited ballast" days. II will happily
trade my 27 for the 29, V2C, JS1 or Antares of anyone going to Hobbs
nationals who is worried about this.

John Cochrane