I opted for 3/4" IPS 100 PSI NSF-rated black polyethylene pipe for my irrigation main line, since it's rated for potable water service and holds up better than rigid PVC against Denver's freeze-thaw ground movement. The flexible HDPE resists rot, corrosion, and pressure surges, with barb connections for easy fitting to valves and emitters, and its 100 PSI rating gives plenty of headroom over what my regulated drip system needs. It's buried to 12".