Place the rice into a large mixing bowl and cover with cool water. Swirl the rice in the water, quickly drain the rice and repeat until the water is clear. This will take 3 to 6 rinses.
Drain the rice in a colander.
Combine the rice, kombu, and 2 cups of water into a medium saucepan* and place over high heat. Bring to a boil, uncovered. Reduce the heat to the low and cover. Cook for 15 minutes.
Remove from the heat and let stand, covered, for 10 minutes. Discard the kombu.
To make the sushi vinegar mixture combine the rice vinegar, sugar, and salt in a small bowl and heat in the microwave on high for 30 seconds.
Transfer the rice into a large mixing bowl, Use a nonmetallic bowl to prevent any interaction with the rice vinegar. Add the vinegar mixture. Fold the mixture through the rice using a slicing motion, being careful not to crush the rice. Try to coat each grain of rice with the vinegar mixture.
Allow to cool to room temperature before using.
Sushi rice can also be made in a rice cooker using the 'white rice' setting.
Kombu is a great addition if you can find it. As you can see from the pictures I didn't have any on hand. Most major grocery store chains carry it but is often sold out.