Cook onion and garlic in oil in a wide 4- to 5-quart heavy pot or deep skillet over medium heat, stirring, until softened, about 3 minutes. Add rice and cook over medium-high heat, stirring, until pale golden, about 5 minutes, then add broth, water, and 2 teaspoons salt and bring to a boil. Cover tightly and cook over low heat until rice is tender, 18 to 20 minutes. Let stand, covered, 5 minutes, then fluff with a fork.