What is the standard winterization practice for an in-ground irrigation system in freezing climates?

• A. Only drain above-ground lines, leave underground lines full.
• B. Use chlorine to winterize.
• C. Leave all water in lines to prevent freezing.
• D. Drain or blow out all water from lines, isolate zones, and insulate above-ground components as needed.

Answer: (D)

Winterizing an in-ground irrigation system in freezing climates means removing all water that could freeze in the pipes and protecting components that sit above ground. The standard practice is to drain or blow out every water-filled portion of the system, isolate the zones so no water can move between parts or remain pressurized, and insulate any above-ground components like the backflow preventer, exposed valves, and the controller enclosure as needed. Using compressed air to blow out the lines is a common method after depressurizing the main supply, and draining low points helps ensure the water is fully removed. Leaving water in underground lines or using chlorine isn’t an effective winterization method—the former risks freeze damage and the latter isn’t a standard protection against freezing. This combination of draining or blowing out water, isolating zones, and insulating above-ground parts best prevents freeze-related damage.