Water Algorithm

This is an implementation of the water fill problem.

Example:

Given a grid, with columns along X, how many cells of "water" can be filled, considering runoff:

Example Grid

          _
         | |
 _       | |         _
  |      | |        | |
  | _  _ | | _    _ | |   _
  |  |  |  |  |  | |  |  | |
 _| _| _| _| _| _|_| _| _|_| _

Result: 14

Note: the bottom is solid, but the left edge and right edge are open (there are no walls).