Ergatta and Hydrow are both high end rowing machines. While Hydrow focuses on personal training and coaching, Ergatta has an approach that's slightly more competition focused.
Perhaps the biggest physical difference between the two machines is that Ergatta uses water resistance, while the Hydrow uses magnetic resistance. This means that you won't choose specific resistance levels on the Ergatta like you would on the Hydrow. Instead, the pace of your rowing will naturally increase or decrease the resistance you feel. For a more detailed look at how these two rowing machines compare, you can check the chart above.