Past experience with this puzzle means that he is referring specificalyl to squares: a 151x1 grid of water with the occaisional 'knob' (shaped like a vine, essentially) is fine; it's only the presence of a 2x2 square that violates the rules.
ZM, if I may suggest a solution? Simply eliminate the 'or larger' from the instructions. It is redundant and apparently serves to muddy the issue. Saying that the water cells must not comprise any 2x2 grids of wtaer should suffice.