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.
The rowing machine itself is unlike any other on the market with its patented water filled flywheel. It is hard to exactly copy the action of a scull on the water, but the mechanics of the flywheel spinning in water comes in a close second on dry land. The fact that the water is 800 times denser than air means that there is no need for any extra resistance or dampening that you will find in normal air rowers. The faster you pull, the more resistance is generated giving it infinite variability. However, if you want to be able to practice rowing with a faster stroke, you will have to reduce the amount of water in the tank unlike an air rower where you just have to adjust the baffle.