John Duke, creator of the WaterRower, was inspired to try his hand at invention while working at a subsidiary for U.S. Steel. He wanted to make an indoor machine that felt as much like real rowing as possible, with a focus on aesthetics. It took him two years to get the design right, moving past failed ideas such as a flipper in the tank instead of a clutch. What began as a series of doodles at his desk turned into a sculptural piece of exercise equipment that upends expectations in two ways: by bringing water indoors, and by looking elegant and artful when stored.
This type of machine provides a smooth action with little wear and tear to the mechanism, and the flywheel itself could help to keep you cool as you work out. It's worth noting that although water rowers aim for a realistic rowing feel, competitive rowers often use air rowers for land training. They tend to be less expensive than water-powered rowing machines, as well.
For a third option, you can look to hydraulic machines, which use pistons to generate resistance. Hydraulic rowers are quiet, and they also tend to be smaller and cheaper than other kinds of rowing machines, but you won’t get the same smooth rowing feel, or the consistency of resistance, that you would get with an air or water rower. What's more, reviewer after reviewer has found them unreliable and high-maintenance.