This event, which will be held from 6:30 to 9 p.m., is sponsored by NESACS, the Town of Barnstable, the Cape Cod Commission, and PID Analyzers, LLC. The topic of the Cape Cod Science Café is Protecting the Cape Cod Water Supply. The keynote speaker will be from the Woods Hole Oceanographic Institute. There will be additional speakers from the Barnstable County Department of Health and Environment. Soft drinks and light refreshments will be provided.