A backwater valve is a backflow prevention device used to prevent outbound water through a dwelling's drain pipes from re-entering -- "back flowing"—into a home. The valve contains a flap that allows water to exit the home, but closes to prevent the back flow into the home.[1]

Back flow valvesprinkler

Backwater valves commonly activate when a city's sewer lines are unable to handle a large amount of falling precipitation; this puts homes that are tied into the storm lines at risk of having water back flow into them.[citation needed]

Are you aware that in order for you to renew your Massachusetts Plumbers/Gasfitters license you must complete continuing education in accordance with 248 CMR section 11.04? This entails 12 hours of class time for plumbers or 6 hours of class time for gas fitters for each renewal cycle. Seating is Limited Contact course instructors John MacDonald or Dave Brogan to reserve your space. All course material provided. $100.00 for plumbers (6 hours) $60.00 for Gasfitters (3 hours) Classes will be held on one weeknight (5 PM-11 PM) and  (Saturday 7 AM-1 PM) per month. Must have picture ID and valid Mass Plumbers/Gasfitters License! If you are more than 10 minutes late you will not be able to attend the class ! Course material and instructors approved by Massachusetts State Plumbing Board. Two Instructors Per Class. Mission Statement: Standardize interpretation and enforcement of the Massachusetts Plumbing Code, Clarify code, minimize grey areas, help strengthen the plumbing industry, and communicate industry changes assist the Plumbing Board and communicate to all local levels.