The other consideration is how water is heated.

Not entirely sure how hotel hot water is heated (centrally in a huge boiler/heater, tanks distributed throughout the property, or banks of instant heaters). We've all run into hotels where the water is barely warm if at all and/or take a long time to warm up sufficiently.

Not to mention that Europeans are said to bathe less frequently than North Americans so water usage isn't that much of a cost issue.