So far I have used 3 different types of auto watering system.
First one below I got from ebay with the irrigation system that came with it all that for less than £20. sounds good but the battery life (it use 2 AAA size batteries) was rather shocking as it lasted around 2 weeks then it stopped working completely!! The system goes on shut down when the battery life is low. Otherwise value for money as it came with a complete micro irrigation tubing.
All these water irrigation timers need to be connected to the mains water tap as it needs the water pressure high enough to push the water thru the pipes. There is not much water timers around that runs directly from the water butt. I would wonderful if you are going away and not having to worry leaving a water tap running unattended. I told my neighbour about the automatic irrigation is on so that they can turn off the tap if there is any excessive flooding in the garden.watering system