A schematic may not help as lines are not routed with direct correlation to the schematic.
Your best bet is to start at the bathroom sink and follow the hot and cold lines towards the water heater. The cold water will enter the heater at the bottom and the hot exit at the top. If the lines going to the kitchen have been cut off between the bathroom sink and the heater you will have to go to the kitchen sink and blow back through the lines to determine which is which. Once defined they are just Teed into the lines you have defined above.
Hopefully the shower has not been touched and come off the bathroom sink lines.
WBCCI 12156 AIR 3144 WACHUNG TAC NJ6
2004 Excursion 4x4
1991 34 ft. Excella +220,000 miles, new laminated flooring, new upholstery, new 3200 lbs axles