Bring water to a boil in a medium saucepan. Add rice and salt; cover, reduce heat, and simmer 15 minutes. Remove from heat, and let stand, covered, 5 minutes or until liquid is absorbed.
. While rice stands, melt butter in a small skillet. Add onion; sauté 4 minutes or until tender. Remove from heat; stir in tomato and lemon juice. Add tomato mixture and basil to hot cooked rice; toss gently. Serve immediately.