The present application relates to a water system that includes a prefabricated fitting tee for use with a water heater. The prefabricated fitting tee includes a fitting tee body that has a first port, a second port, and a third port. The first and third ports can be aligned along a main axis and the second port can be aligned along an axis angled relative to the main axis. The fitting tee body defines an interior passageway that is in fluid communication with the first, second, and third ports. One of the first and second ports is configured for connecting to a water inlet conduit for supplying water from an external source, the other one of the first and second ports is configured for connecting to a pressure relief or pressure absorption mechanism. The prefabricated fitting tee does not include a check valve for preventing flow from the first port to the third port and no check valve for preventing flow from the second port to the third port. A swivel nut can be rotatably mounted at the third port of the prefabricated fitting tee to provide an interconnection to the water heater. When the swivel nut is in a first condition, the swivel nut allows the prefabricated fitting tee to be rotated relative to the water heater about the main axis to allow a rotational orientation of the second port to be established. When the swivel nut is in a second condition, the swivel nut clamps the prefabricated fitting tee in the established rotational orientation.