how to go from 1/2 copper to 1/2 polly water line?

If you are talking about a 15mm copper pipe that you wish to connect to a 15mm plastic barrier pipe, a normal 15mm straight compression connector will do fine. All you need is the correct steel inlet that you push inside the plastic pipe, then you connect up, with the olive, as normal. You can actually push a plastic connector straight onto copper pipe if you want. Check out the jg speedfit range, on the web, for tips.

John
April 2009