I'm working on a different approach to RD. I found the old one poorly thought out and buggy as shit, so I started making one from scratch. The problem is that the resources in RD have always been abstract values with very little importance to the player, since EVERY resource acts like electricity.
I'm doing it by making the dev define a "header" type dealie so that other parts of the script have a fairly low-cost reference point for dynamic factors, like rate of flow, density, that kind of thing. If you go to
www.gamedev.net, there are no shortage of fluid dispersing algorithms, and they take so little to run that there's really no point in having resources propagate instantly.