Sift the flours into a large bowl and make a well in the center. Add the eggs, water and 1 teaspoon of salt to the well. Using a fork, gradually incorporate the flour, tossing and stirring to blend; the dough should be smooth and very soft. Cover and refrigerate for 1 hour.
Bring a large pot of salted water to a boil. Working with 1/2 cup of the dough at a time, pat it into a 3-inch square on a small cutting board with a handle or on the back of a square cake pan. Using a moistened metal spatula or chef's knife, cut and scrape 1/4 -inch strips of dough into the simmering water. Cook the spaetzle, stirring, until they float to the surface, about 2 minutes. Using a slotted spoon, transfer the spaetzle to a colander. Repeat with the remaining dough, moistening the spatula when the dough begins to stick.
In a large skillet, melt the butter. Add all of the spaetzle and sauté until lightly browned. Season with salt and serve hot.
Semolina flour is available at specialty food stores.