To trade off no longer tracking fluid levels in a tile, instead watching "blocks" of water, in the rewrite we're simulating the grid with a little finer grain: what was one tile before is now effectively two tiles, stacked vertically.
This means that the boulders, from before, will have to have special support to handle being larger objects than the tile resolution. Also, in the updated design, actors like the player will no longer exist as entities outside the grid, but in fact will be special types of tiles, which is a more "organic" representation that significantly changes a lot of subtle things.
The result is, I'm working on a new type of entity: the Multitile entity.
Multitile entites have one tile that's considered to be the "key" tile. This is the one that gets turns, the only one that gets added to the cellular queue; the others are just along for the ride. A previous project (one of the things I had to pick up for money, that has delayed In Profundis for so long) also used a cellular system that used multitile entities. I learned a lot from that concerning how to simulate these kinds of objects, and the possible pitfalls.
So you see, I don't think all that time was wasted, I think it's a subtly wiser programmer that's working on the problem now.