Heat broth and water in a small saucepan over moderate heat until hot, then crumble saffron into liquid and stir. Remove from heat.
Cook onion in butter in a 2-quart heavy saucepan over moderate heat, stirring occasionally, until golden brown, 5 to 8 minutes.
Add rice and cook, stirring, until fragrant and pale golden, about 3 minutes. Stir in saffron broth, salt, and pepper and bring to a boil. Reduce heat to low and cook, covered, until rice is tender and liquid is absorbed, about 18 minutes. Remove from heat and let stand, covered, 5 minutes, then fluff rice with a fork and fold in almonds.
