HDPE Water Pipe From okay Plastics. At okay Plastics, we offer the following HDPE water pipe options: 3/4″ to 54″ diameters with pressure ratings up to 335 psi. Blue lor stripe for easy identification. IPS, DIPS, SIDR and CTS sizes. Solid blue CTS for water service tubing and SIDR for water wells. FM-approved capabilities.