Water age is the time spent by a parcel of water in the network. It provides a simple, non-specific measure of the overall quality of the drinking water supplied. New water that enters the network from reservoirs or source nodes enters with zero age. As this water moves through the pipe network, it breaks up and mixes with parcels of varying ages at pipe junctions and storage facilities. EPANET provides automatic water age modeling. Internally, it treats age as a reactive constituent whose growth follows zero-order kinetics with a rate constant equal to 1 (i.e. every second the water becomes one second older).