Bring the water (3 1/2 cups) to a rolling boil. Add the salt and margarine, stirring to melt. Using a wooden spoon, add the cornmeal very gradually, while stirring constantly in the same direction.
Simmer over low heat, stirring frequently, until it thickens and starts to pull away from the sides of the pot, about 35-40 minutes. Serve hot.
If desired, while mamaliga is still hot, add more margarine, cheese, sour cream and herbs. Mamaliga can also be served with a dollop of sour cream. Mamaliga can be poured into a pan. When cool, it can be flipped out onto a cutting board, cut into squares and sautéed in butter until crispy.