Things You'll Need
Black felt tip pen
CPVC "T"-shaped coupling
Plastic water pipes are made of CPVC plastic, are white in color, and for household use usually come in 1/2- or 3/4-inch diameters. Adding a new water line to an existing line (or splicing into it) is a fairly simple process that requires fitting a new coupling (connector) into the line. Once glued into place, the new water line is then also connected to the coupling. This will allow water to flow through the new pipe--as well as the existing one--to a new water outlet (faucet, toilet, etc.).
Turn the water off at the house's main shut-off valve. Use a black felt pen to mark the plastic pipe in the location where the new pipe is to be spliced.
Cut through the pipe at the mark, using a hacksaw. Make sure that the cut is straight. Remove any burrs from the cut with a work knife, and wipe each side of the cut with a rag to make the area dry.
Apply primer to the pipe on each side of the cut--use PVC primer. Also prime the inside of a CPVC "T"-shaped coupling. Wait for the primer to dry (usually 1 minute).
Cut a new piece of CPVC pipe to the required length, and prime both ends.
Apply PVC glue to the existing pipe on each side of the cut, as well as one end of the new pipe. Also glue the inside of the "T"-shaped coupling. Push the existing pipe on each side of the cut into the coupling's ends. Push the new pipe into the remaining end of the coupling--hold for 30 seconds.
Place an old towel beneath the existing pipe when cutting into it to soak up water. The other end of the new pipe is ready for new pipe and couplings to be glued to it, so it reaches to the new water fixture. However, if this work is to be done at a later date, simply prime and glue a CPVC end cap to this pipe. Once the glue has dried (usually a minute), the water can be turned back on at the main shut-off valve.