The water heater is set up to use a double pole breaker in the U.S. to create the 220v needed with 2 hot wires, and a ground wire. However, overseas the incoming voltage is already 220v, and doesn't need to be created using the double pole breaker. I am unsure how to wire the unit over there because of the 2 hot leads on the heater, instead of a hot lead and a neutral lead at 220v
I wouldn't wire this in Europe. As I mentioned in a comment, I used to work for ETL, which is an NRTL (Nationally Recognized Testing Laboratory). ETL evaluates and tests devices for compliance in the markets the manufacturer plans to sell the device in.
Below is an image from the manual. You will notice the C and US next to the ETL circle. This means the product was evaluated and found to be in compliance for Canada and the United States. There would be an E if it was accepted in Europe.
What does this mean? It means that this device has not been evaluated and tested to Europe's standards. Europe's utility may have the voltage you need to run the water heater, but their utility is 50Hz, not 60Hz. This difference in frequency can be bad for internal control transformers and other control devices.
Another problem is that to wire the device in an European panel, you would need to wire L1 of the water heater to line of the panel, and L2 to the neutral of the panel. The control system isn't expecting a grounded L2 connection and that may cause problems. Also, the manual clearly states that the use of a two-pole breaker is required.
I know you were probably trying to save money by using this water heater, but it would be a bad idea to use it. Play it safe and get something designed for use on Europe's utility.