The Marlborough Brook Filter Beds are a series of water filtration beds near the mouth of Marlborough Brook, where it enters Sudbury Reservoir near the town line between Marlborough and Southborough, Massachusetts. The filter beds were constructed in 1895 as part of the reservoir construction to improve the water quality of Marlborough and Walker Brooks, and are the best-preserved of two such facilities built as part of the public water supply serving Boston and surrounding communities. The site was listed on the National Register of Historic Places in 1990.