I'd like to start capturing rainwater and using it to help supply the irrigation system I already have. It's a standard Rainbird sprinkler system that runs on full pressure water supplied by the city. From what I've read, I'd probably need a pump to get the rain water pressure to be high enough to use for the sprinklers.
I won't be able to store nearly enough rainwater to run the sprinklers entirely off of rain water. I think I'd be lucky to be able to store enough for one watering.
So what I'm stuck on is: is there anyway to plumb this so that the sprinklers would run on rainwater when it's available, but back-off to the regular domestic water when that runs out? Or supply it from both sources so that the domestic water continues to provide water after the rainwater runs out?
Is there some sort of Y-fitting that is able to give one supply priority? Or maybe it could be done with some check valves? Or something totally different?
Edit: The answers so far involve building a rainwater only supply system, and then using a float to add utility water to the tank when it's almost empty. I'd prefer not to do that since it would seem to put more stress on the pump and increase the risk of flood if the float valve fails.
Best Answer
Simplest 100% legal way would be to make it use rain water directly from storage containers, and then a float valve that fills the rain barrel with city water if the water level gets below a certain level. This would also allow you to maintain an airgap between potable and non-potable water sources.
You're losing the free water pressure from the city water, but you already will need a pump large enough to handle the unpressurized rain water so you're using the pump for both water sources.
Also hook up a 24 VAC electric operated water solenoid valve that is controlled by your irrigation controller that shuts off the city water to the float valve to make sure that if the float valve gets stuck open that the water won't flow if the irrigation system is off. Maybe getting a 120 VAC one would be better if you make it operated by the same control that turns your pump on and off, instead of with your irrigation controller zones.
Typically that would be called a master valve in an irrigation system, but this is a little different but mostly the same idea.