If two water particles are touching, they combine into 1 object, which will split if hit hit with a certain amount of force, therefore less calculations are needed. (A whole river would still be ONE object, but would still splash and stuff if hit)

The combined water particles as an object would have to act like goo and be able to move or alter it's shape, if two particles join angle and velocity of both would be calculated to form the new one.

Use the Phun method of water which uses a bunch of circles that are shaded to look like water. You could make them combine to form bigger circles when stationary and break apart when they move faster. Making the terrain act a similar way might allow terrain gibbing and more efficient physics.

My idea was to make gibs that stick together and break into smaller gibs extremely easy. Also, they'd have to be bouncy.

edit: Also I have already made fully piling, pooling water, but CC cannot handle the insane amount of physics, and cannot cope with ANY piling material, spam a load of dropships and you will see that they EAT through the ground, that happens whenever anything is pushing anything else, and that is what happens when stuff piles.