Mix the water, grits, and butter in a large saucepan. Bring to a boil over medium heat. Reduce the heat to low, cover, and simmer for about 45 minutes or until thick. If the grits become too thick, add more water.
Preheat oven to 350F. Grease a 9 X 13-inch pan or 8 individual baking dishes.
Saute the sausage, breaking it into small pieces. Set aside. Saute the onion in the fat from the sausage. Drain. Add the onion to the sausage. Add the butter, eggs, and cheese to the grits. Then add in the onion/sausage mixture. Add the parsley and mix well.
Pour the mixture into the prepared dish (or dishes). At this point you can refrigerate the casserole for up to two days before baking. And it also freezes well.
Bake for one hour (30-45 minutes if you are using the individual dishes).