A water main break left 1,500 Co-op City families without water Monday.Public safety workers say the break, which happened sometime around midnight, took place behind Building 4. Residents at three of the buildings in the complex say they have had to deal with water problems in the past. Maintenance crews, who have been working to get the water restored, say they are investigating the cause of the break. The building manger says water should be back on by the end of the day.