@daveforge, you may need to consider latching water valves like this one:
These only require power when they change states. If you battery power the whole thing, you will need to consider solar charging to maintain your batteries to run both the Photon and valves. Operating 5 valves simultaneously will require about 2.5A at 5V, requiring a large enough battery to supply this power without drop in output voltage. You may want to consider a 12V system instead, reducing the current requirements.
If you power from 12 or 24V supply (wall plug), then you will need to step down the voltage for the Photon and power your valves directly from the 24V supply.