This is how it's done. This is the mechanical room in a house in Center City we designed and built. All the copper supply lines are insulated and lead to the hot water heater and to two PEX manifold systems where each fixture has it's own individual shutoff. The Cross-linked Polyurethane lines branch out and feed the house.

PEX system - Cross-linked Polyurethane systems (PEX) are superior to copper supply lines. Each fixture is a home run to a manifold, so hot water gets to the fixture faster, and they are independently fed, so when you flush the toilet the shower doesn't become scalding hot. The main benefit for me is that there are no connections behind the walls and therefor they can't leak!