Tai Tam Byewash Reservoir, part of the Tai Tam Reservoirs, is a reservoir in Tai Tam Country Park, Tai Tam, Hong Kong Island, Hong Kong, and has a water storage capacity of 22.4 million gallons.

[4][5] Its dam and the valve house built at the centre of the dam are listed as declared monuments while the ruins of the Tai Tam Byewash Reservoir senior staff bungalow and the workmen's quarters as well as the Tai Tam Reservoir Red Brick Building are classified as Grade III historic buildings.

[6][7][8] The water storage capacity of Tai Tam Upper Reservoir is still inferior to the population growth.

As Hong Kong Island lacks land that can be developed into a catchment area, the government decided to expand the water supply system of Tai Tam Valley, implement the second phase of The Extension of the Tai Tam Water Supply System and to construct the byewash Reservoir to collect the freshwater overflowing from the upper reservoir.

There is a short pier between these two dams and the reservoir was completed in 1904.