hook up of an irrigation system with out a proper backflow device and to a outside hose bib is illegal and non code in every public water system and jurisdiction im aware of and poses a health risk to any water system as it creates a cross connection where if under the right conditions, say loss of pressure, water from the irrigation system and whatevers been laying in your yard can flow back into and contaminate the potable water system,it happens more often than you would think. at the minimum every hose bib should have a vacuum breaker installed but... ALWAYS CHECK LOCAL CODES ECT.BEFORE STARTING ANY PROJECT, PARTICULARLY PLUMBING.