This has seriously taken me about 8 hours of coding to get the bloody thing to work.
But DF now has a basic irrigation system. :) Plants will still check for water within 4 blocks, but they also check for irrigation pipes within 3. I will be doing a whole system with this where you need a pump block next to water, and then pipes connected to it and they WILL check to make sure there is a connection... hopefully.
And no, the plants don't eat the blocks like they do with water. :)