In article , Broadback
wrote:

I have a Gardena Water computer, the instructions say it works with a
minimum dynamic operating pressure of 1 bar. What sort of pressure do
you get from a water butt, say mounted a foot above ground level and 1/3
full? It would be nice to use it while away, as I am now on a water
meter I can just see a problem occurring while away and water streaming
out!

You'll need a submersible water butt pump to make it work (about £40).