Stir together the water and sugar in a small saucepan. Bring to a boil and add the walnuts. Boil for 2 minutes, then drain and place walnuts on a cookie sheet to dry. Whip egg whites in a medium bowl until foamy. Stir in the mochiko until it has a pasty consistency. Heat the oil in a heavy deep skillet over medium-high heat. Dip shrimp into the mochiko batter, and then fry in the hot oil until golden brown, about 5 minutes. Remove with a slotted spoon and drain on paper towels.