If you connecto an irriagation system to potable water (house water, drinking water, ect.) you will need an approved back flow device.
That is for your safety.
Description: Double Check Valve Assemblies
Size Range: 1/2 to 3 in. (15 to 80mm)
Series 007 Double Check Valve Assemblies prevent the backflow of contaminated water into the potable water supply. It consists of a bronze (1/2 to 2 in) or fused epoxy coated cast iron (2 1/2 to 3 in) body construction that is easy to maintain and service. Series 007 is ideal at referenced cross-connections identified as non-health hazard applications. Check with local inspection authorities for installation requirements. Maximum Working Pressure: 175psi (12.06 bar).