Pressure Sensitive Water Valvle

I want to implement FarmBot into a rain water system, but I don’t get a lot of rain. What I would like to do is join my rain water system with my connected utilities via pressure sensitive valve. Does anyone know where I can get something like this? Basically it would use the rain water until the pressure drops too low, then the valve would switch until the rainwater system builds enough pressure.

A quick search found this.