Controlling large amounts of water can be a pain. One wrong move or error in planning and you can find yourself with lots of generated source blocks to remove. One simple way around this would be a rule that prevents water source blocks from being generated over some types of (spawnable) solid blocks (such as inverted stairs). This would simply allow Minecrafters more control over where they do and do not want water source blocks to be generated. A simple change that could prevent a lot of headaches.