Do you need the Arduino to turn the water on/off, or can that be your host/server?
I'm still trying to figure out what my options are. I have several hundred gallons of rain water/lake water next to the garden. So all I need is the smallest of solenoids to control the gravity feed. Before I was thinking about SSRs (solid state relays), maybe connecting a small pump to my water tank to increase the pressure. Thoughts on control valves for gravity fed watering or SSR + 120v pump?
failure may have a large impact
Thanks gbulmer. I hadn't thought too much about the downsides yet...