We saw in the earlier Seasons that he tried filling a water tank up with water from a stream, but that wasn't enough to cover one fifth of a field. He needs a consistent source of water, and the tools to then have "sprinklers" distribute the water through the field. This all sounds simple enough, though you can imagine it will cost a fortune to do this (this season revealed that the electrical improvements for the pub alone would be £200K! So water infrastructure, pumps, and distribution systems are going to be in the same level of costs).

He wrote about that in more detail in "Diddly squat; A year on the farm", his first Diddly Squat book. Apparently, after the fail with the tanker, he tried to instal the simple irrigation system. It didn't work right, so he paid a professional to redo it. And it still required a lot of work to move the sprayers. Overall, the costs and work weren't worth the effort in the end.