So I've seen ideas for this before on the internet, but as always, it took a little while to come to fruition.
A water play activity board. Made of all recycled materials! The board it's on is actually four pieces of the ply we had up on the windows when we renoed them in November last year. I knew they would come in handy. I liquid nailed them together and then did some reinforcing with some bolts we found in a tool box. Not sure what we got them for originally, but they were excellent for this.
Again, I painted it with some more of the leftover window paint (still have a half a tin! Will it ever end?) All of the containers are recycled ones that I staple gunned on. Fabulous. The girls love it. It's a little high level for them at the moment, but they do love pouring the water and getting wet.
The one downside is that when there is no water, the next logical step for the girls (and other visiting children) seems to be that sand should be poured in. It's not the end of the world, but it is mildly annoying. Anyway, the whole thing is fixed to the fence with only four screws, so it's easy to remove, which will probably happen come winter.
For now, long live summer and water play!