I built my own watering system for the greenhouse, 12v battery powered with a water supply from a big poly tank , a motorized valve was originally used, I did publish the design in an electronics magazine in 2006 (EPE) , however some specialist knowledge would be required to build it. Later I found a switched pump was a more effective method , this came on as per a program , in the growing season about 10 secs every 4 hours , ( 6 tom plants ) between 10am to evening time, another benefit is adding feed to the water and the water is same temperature as plants. its still working.