Residents in Dorchester and Mattapan are urged to boil water before drinking this afternoon after a water main break in Weston, MA prompted the Mass Water Resources Authority to activate its back-up water supply. The MWRA says that water now available in Boston and surrounding communities east of Weston is safe for bathing, but not for drinking- unless the water is boiled first. The agency is urging residents to try to conserve water use. Updates will be posted at the MWRA's emergency website.