The tank of the WaterRower Oxbridge Rower is made from polycarbonate, one of the strongest plastics available. It is virtually indestructible. The tank is sealed and can be filled with municipal water via a small opening closed by a stopper. This water typically contains enough chlorine to remain clear for some time. After exposure to light, the chlorine will degrade; the chlorine tablets should be added periodically.
Water machines are generally quieter than air rowers - you can still hear the water moving in the tank, but users tend to find this a pleasant ambient noise. Water rowers also tend to require little maintenance. Because there's a tank full of water involved, however, these can be very heavy, and larger than most other rowers: if you have a smaller home, a less-than-permanent workout space, or you move frequently, these might not be best for you. And because they're so high-performing, they do come at a high cost.