The Pennichuck Brook Watershed occupies land in five southern New Hampshire towns, including Nashua, Merrimack, Amherst, Milford, and Hollis. The primary water supply consists of about 195 acres of water in a series of chain ponds that includes Harris Pond, Bowers Pond, and Holts Pond. There are also several other ponds in the watershed that store water upstream from the water supply ponds. The overall watershed area is 17,300 acres with 10 subwatersheds of roughly 1,200-3,200 acres each. After flowing through the chain ponds, Pennichuck Brook ultimately joins the Merrimack River.