The Connecticut Water Co. and the South Central Connecticut Regional Water Authority (RWA) have partnered in a $40 million deal to acquire and split up the 11,500 customer water company, Birmingham Utilities Co. of Ansonia. Under the sale, the New Haven-based RWA gets Birmingham’s 9,500 customers in Ansonia, Derby and Seymour. Connecticut Water paid $3.5 million for the assets of Birmingham’s Eastern Division, which has 2,200 customers in 15 towns, including Ashford, Colchester, Manchester and Hebron. The deal is expected to close in six months.