The glue I use on water lines in the plumbing trade is made by Oatey called Rain or Shine. Always use primer, beforehand. And it doesn't take much, like jhnrb told you. Clean pipe AND fitting, then add glue to pipe AND fitting then give it a quarter turn. This gives the glue enough friction to heat up and make a very good bond. Hold your fitting in place for a about 10 seconds, so it doesn't back out. It happens to the best of us! If you have to do any repair work, you'll like rain or shine because, it will set up even if it's wet. That can save you a huge mess and lives. There is nothing wrong with using it from day 1, though. It has a little more give/flexibility when it's dry than ordinary pvc cement. Ordinary pvc cement is not designed for very much pressure. We use it mostly on drainage. In my experience, I feel most comfortable using Rain or Shine on ALL water lines. And in use exposed to the elements in this hobby/trade, I'll say it's the best anyone could use.
Burney
Journeyman Plumber UA Local 17