Rinse the rice in a sieve under cold running water until the water runs clear, drain well. Add the rice to the pan along with the water and salt, leave to absorb for approx. 15 mins. Bring the rice to the boil (uncovered), reduce the heat, simmer until the water has evaporated, leaving small indentations on the surface of the rice. Cover and leave to fluff up over a very low heat for approx. 10 mins. Mix in the vinegar, leave to cool.
Quarter the rice, shape each portion into a maki roll. Cut the nori sheet into 4 strips, wrap a strip around each portion, arrange on a platter. Press the rice down to approx. 5 mm below the rim of the surrounding nori strip. Spread the salmon roe on top of the maki, serve with the soy sauce, wasabi paste and ginger.