Put the rice in a large bowl and cover with lots of water. Stir the rice in the water with your hands, then pour off most of the water and agitate 10 to 15 times by quickly moving your hand back and forth, in a waving motion, swishing the rice against the bottom and sides of the bowl. Rinse the rice several more times, until the water that drains off is almost clear. Transfer the rice to a colander, and let drain for 1 hour, undisturbed. Transfer the rice to a rice cooker, add the water, cover and cook as directed by manufacturer’s directions.
While the rice is cooking, bring the rice vinegar to a boil in a small saucepan, then remove from the heat. Add the sugar and salt, and stir until dissolved. Allow to cool to room temperature.
When rice is cooked, allow it to remain in the rice cooker for 10 minutes. Transfer the rice to a large shallow mixing bowl (traditionally a wooden tub, called a hangiri), so that rice forms a mound in the center of the bowl. Using a diagonal slicing motion, gently cut into rice with a wooden paddle (called a kijakushi), and pour the cooled vinegar mixture over the top of rice. “Cut” the rice several times to evenly distribute the vinegar mixture, then allow to cool.
Gently turn the rice over from time to time with a paddle so that rice cools evenly. You might want to consider using a fan if time is of the essence. When rice has cooled to body temperature, it is ready to use for sushi rolls. Rice can be kept at the proper temperature by placing it in an insulated container such as a small ice chest, covered with a damp kitchen towel.
Makes enough rice for at least 7 large rolls (Futomaki)