Question

The water isn't scarcely enough for all three of us. Fix the double negative.

Answer 1

The water is scarcely enough for all three of us

Answer 2

Either 'The water is scarcely enough for all three of us' or 'The water isn't enough for all three of us.'

I think the first sentence is better because it's closer to the original, but both get rid of the double negative :)