A 125-pound person moving at an average pace for 30 minutes on a treadmill will burn roughly 250 calories. However, they aren’t able to take advantage of this after-burn effect. The same person rowing vigorously will burn around to 250 calories but will have less stress placed upon their joints and continue to burn calories after the workout has ended. Rowing machines have been shown to burn on average 800 calories an hour if you work harder and are slightly heavier.
Of the four types of rowing machines or ergometers, water rowers are best at reproducing the sensation of on-water rowing. Their stroke cycles hold true to the dynamics of real paddling, and each stroke is punctuated with a splash! Water rowers have sliding seats to allow full-body cardiovascular workouts. (With cheaper rowing machines, in contrast, the seats don’t move.) These fitness machines tend to feature high quality parts and can last a lifetime.
Rowing machines were first used in Archaic Greece. Chabrias, an Athenian military general in 4th Century B.C., invented wooden rowing simulators for his inexperienced oarsmen. This enabled them to learn technique and timing before stepping foot on actual water crafts. And it must have worked — Chabrias successfully led numerous naval attacks against the Spartans.

Another negative point for me is the angle of the seat. Unlike the Concept2, it has a slight backward angle, which makes it easier to maintain good form at the end of the stroke. Given that the Waterrower has greater resistance at the catch, it puts more pressure on the lower back at this point making it uncomfortable for people like myself with lumbar spine problems.
If the machine is to be housed on a wooden floor you will need a mat beneath to reduce vibration and also noise. If space is tight, the hydraulic options are usually the smallest. It's also worth checking your floor can take the weight if you're going for one of the bigger, heavier models. For most, this shouldn't be a problem, if you have any doubts get a surveyor to check as it could be a very expensive mistake!
First of all, if you're considering rowing, just do it. It is by far the most enjoyable and beneficial exercise I have ever tried. I've made huge strides with both cardio and muscle fitness with the WaterRower, and it's so enjoyable I look forward to exercising each day. Yes, it is more expensive than most other rowing machines, but when you compare it to a lot of other types of exercise equipment, it's actually pretty reasonable. When you also compare the exercise benefit you get, it's a bargain.