A modular water based heating and cooling system for providing chilled or heated water to terminal devices in a building to heat/cool individual zones in the building. The system includes a flow control device in fluid communication with a riser chilled water supply line, a riser chilled water return line, a riser heated water supply line, and a riser heated water return line. The flow control device includes first control valves and second control valves. Terminal device supply lines extend from the flow control device and are connected to respective first control valves. Terminal device return lines extend from the flow control device and are connected to respective second control valves. The first control valves and the second control valves cooperate to supply required chilled water or heated water through the terminal device supply lines to terminal devices based on the cooling/heating requirements of the terminal devices.