The system works with a single flow of water, just fill the tubing from the top and the water will start running throughout the whole facade. (Both sides have different pressures, by adjusting the top valves you can regulate the amount of water depending on the time of the year and the plants). 
Once you have decide in which cell you want to have plants, just need to feel the cells with the seeds and the nutritive layer wihich will depend on the kind of plants. The plants will start growing and you can water them as often as needed, having the option also to empty the whole system by opening the bottom exit.
Here you can see a slideshow of the process:
IaaC 2007-2008 Smaq Workshop
Tutors: SMAQ Sabine Müller - Andreas Quednau
Authors: Rodrigo Langarica , Mariana Paz Castellanos, Monika Szawiola, Erik Thorson
