PVC gravity feed drip irrigation

Drill two rows of holes, each row being about 25° off the top centerline of the pipe. Space the holes about 4 per square side. use a No 60 drill bit so that the nozzles are 0.040" holes (1 mm for you metric folks.).

The beauty of this system is that it automatically meters about 4 cups of water per square. So it will likely dedicate one bucket per 4x4 box. Dumping one bucket of water into the irrigation bucket is certainly faster than fighting your way through the plants to ladle water onto 16 separate squares.

From : Squarefoot