Bring water and salt to a boil in a heavy saucepan. Add rice, stirring well. Cover; cook over low heat 25 to 30 minutes.
Grease a 1 1/4-quart ovenproof ring mold. Pack cooked rice into mold; pour butter over top. Place in a pan of hot water. Bake at 350° for 20 minutes. Loosen edges; unmold onto a serving platter.