Reservoir water supply has been an important way to settle the shortage of water resource, especially for the urban water supply. The water quality and trophic level were investigated in a newly constructed reservoir—Feilaixia Reservoir from 2001 to 2003. The data showed that concentration of main nutrients and phytoplankton abundance are low, and the water quality is good enough to be used as the water source for drinking water. As a very short retention time for the flowing water in the reservoir, the water quality has a little variation in seasons. Feilaixia Reservoir takes an obvious advantage in stable water supply for both water amount and water quality. To meet sustainable water supply, more attention has to be paid to watershed management.