Water and sewer districts are generally operated at the municipal level, providing retail service to residential and business customers, and making provisions for sewage treatment and acquiring water from wells, rivers, or wholesaler. Some local water districts have been consolidated across municipal boundaries and some operate at the sub-municipal (village) level. Running water and sewer service is not necessarily available to all buildings, especially in low-density areas; building owners in these areas must obtain their own water and dispose of their own sewage. The Massachusetts Water Resources Authority provides wholesale water and sewer services to many cities and towns, mostly in Greater Boston, in cooperation with DCR watershed land management. Combined sewers in some areas are being separated to reduce water pollution.