If you purchase them, then they are not "wild", unless illegally sold. Thus, how much "domestic mallards" like the water, compared to other domestic ducks, may depend on how brave they feel about swimming in the water presented to them, at least when they are young. They have no mother to take them right into the water after they hatch, and make them feel secure in it, because she is there to protect and teach them. Instinct wise, though, they should love water and feel safer and happier in it than on land.