In a medium bowl, soak the rice in warm water to cover for 10 minutes. Drain and rinse under cold water until the water runs clear, set aside.
In a heavy saucepan over medium heat, add the 3 cups of water and infuse saffron threads for about 10 minutes warm. Incorporate the rice and bring to a simmer, stirring occasionally, to combine the flavors, 6 to 8 minutes. Add the tomato, onions, garlic, and oil, and stir to combine. Bring to a boil and add the clams. Sprinkle the parsley and salt to taste. Stir once again to combine, cover and simmer over low heat until the rice is fluffy, and the clams have opened about 20 to 25 minutes. Discard any of the clams that fail to open.