New Haven sits on Long Island Sound, and its flooding history shows it. During Sandy on 10/29/2012 the National Weather Service recorded a peak tide of 12.3 ft MLLW, and 1 to 2 ft of water covered Long Wharf Drive and the properties around it. If your basement takes on water, the cause may be tidal flooding, a backed-up drain or groundwater, and each needs a different fix. Before you hire for a backwater valve, sump pump, drain or waterproofing job, ask the contractor to say in writing what they think the cause is and how the work addresses it. Check your insurance first too: the Connecticut Insurance Department says most policies exclude water that backs up through sewers or drains, and suggests asking an agent about a sewer backup endorsement. If street drainage seems to be part of the problem, you can report it to the City Engineering Department by phone or through SeeClickFix.
Source: National Weather Service (NOAA) (source, opens in a new tab)