Place rice and 1 cup water into saucepan and bring to a boil. Cover and simmer on low for 10 minutes, or until most of water has absorbed.
Meanwhile whisk together 2 cups milk with sugar, tapioca and salt. Set aside.
Add milk mixture to rice and stir to combine. Add remaining milk and cook, uncovered, on med-low heat, stirring often, until starting to thicken, about 30 minutes. Stir in raisins, if using, and continue to cook, stirring often, until thick, about 20 minutes.