Add some leftover salmon to the rice (just eyeball it), and then mix it with a fork so the salmon becomes evenly mixed throughout the rice.
Then cut a large square of plastic wrap and rest it over the measuring cup. Lightly spray the plastic wrap with the water bottle, and then sprinkle it with a bit of salt (the water helps the salt stick).
Then spoon some of the rice mixture into the cup (roughly 1/4 cup of the mixture). Gather the plastic wrap up around the rice.
Then twist the plastic wrap, sealing the rice inside, and firmly press the rice into a ball shape.
Unwrap the ball, set it on a plate and repeat the process with the rest of the rice mixture.