CONCORD, N.H. — A plastics company believed to be the source of tainted groundwater in several New Hampshire communities has agreed to provide more than 300 homes with safe drinking water.

The New Hampshire Department of Environmental Services and Saint-Gobain Performance Plastics reached an agreement Tuesday to permanently provide the drinking water to 302 homes in Bedford, Litchfield, and Merrimack. That brings to 752 the number of properties getting help from Saint-Gobain. The state did not say how much the plan would cost.

Saint-Gobain used the chemical perfluorooctanoic acid, or PFOA, at its Merrimack facility. The chemical, used in coatings such as Teflon, has been linked to certain kinds of cancer and thyroid disease.

The company has faced similar problems in New York and Vermont.