Not all leaks happen immediately after cementing a joint.  Check on all joints immediately after pressurizing, 10 minutes, 30 minutes, 1 hour, 4 hours and the next day to ensure the joint has properly seated and sealed.

If working on a water line and the shut off valve is out of sight, always work in pairs.  Phone your partner before you turn the water back on in the case one of your joints did not properly seal.  That way you can stop any flooding before too much damage can be caused.