A quasi-public agency says it’s investing more than $18 million in drinking water projects in Rhode Island. The Rhode Island Infrastructure Bank said the financing is going to the city of Woonsocket, towns of Burrillville and Cumberland and the Providence Water Supply Board.The agency says this will save about $1 million in interest expenses,compared to borrowing from other sources.It says it has now invested more than $500 million in drinking water projects throughout Rhode Island.