I will provide more details after some suggestions are made
That's not the way this works. If you want suggestions you have to provide the specifications of your project.
Would you ask an engineer "Design something for me that does something.."
We need the valve specs: Flow rate , fitting size etc..
We can assume the interface to be anything the arduino can acomodate. Motorized valves come in all shapes and sizes.
Be specific. List your criteria. That's rule #1 for forum posts:
http://forum.arduino.cc/index.php/topic,148850.0.html