Regarding safety, there are a few things to keep in mind. First, you don't want to leave water sitting in the reservoir. A water flosser that isn't well maintained can introduce more bacteria into your mouth, so Dr. Creaven recommends emptying it after each use and cleaning it often. You'll also want to pay special attention to excessive pressure. "Since water flossers utilize a pressurized water stream to remove plaque and debris, it is important that patients don't traumatize their gums with the device," says Dr. Kunen. "Follow the directions of use to prevent any damage to tissues."