When selecting a backflow preventer for an irrigation system, factors to consider include the system pressure, flow rate, and hazard level. Irrigation systems typically require backflow preventers that can handle high pressures and flow rates. The hazard level, which refers to the potential risk of contamination, should also be assessed. For example, irrigation systems used for agricultural purposes may require a higher level of protection than those used for residential landscaping. Additionally, the type of irrigation system, such as sprinkler or drip irrigation, should also be considered.