Place rice in a thick-walled aluminum pot. Fill with water from sink until rice is completely covered. Stir rice by hand to clean the rice of any debris (grain casings, etc.). Drain water completely.
Place on stove, and pour in 3 cups of water. Add in salt and margarine, and turn flame to high. Stir so the salt mixes well and the margarine is broken up/melting.
Once water starts to boil, cover with lid and reduce flame to low. Let cook covered for 18 minutes.
Lift lid, being careful that the steam slides away from you. The water should have soaked into the rice. If water is still visible bubbling above the rice, cover and let continue to cook for another minute or two.
Once water is gone, shut stove off and allow to sit covered for 8 minutes. Remove lid, stir, and serve.