Complex sentence: The Quinapoxet and Stillwater rivers are the two major tributaries to the Wachusett Reservoir, which serves as the primary source of water for 2.5 million consumers in 43 communities of central and eastern Massachusetts.
Split into simpler sentences: The Quinapoxet and Stillwater Rivers are the two major tributaries to the Wachusett Reservoir. The Wachusett Reservoir serves as the primary source of water for 2.5 million consumers in 43 communities of central and eastern Massachusetts.