In a food processor or mixer, cream the butter until fluffy. Add 3 1/2 cups flour, sugar, salt, eggs, flower water and water. Mix until completely combined. The dough should be stiff, just beyond sticky, so that you can handle it without it sticking all over you. You may need to add a bit more flour to get there.
Gather the dough in a ball and divide it in two. Divide each halve into halves and then once more so that you end up with eight balls of equal size. Each of these should be further divided into three balls so you end up with a total of 24.
Roll each ball into a cylinder shape about three inches long. Place these somewhat spaced apart on a non-stick baking sheet (or a greased regular one). Flatten each cylinder somewhat and pinch the ends to form a boat shape. With a sharp knife, slit the boat down the center stopping at about an 1/8 inch from each end.
Leave the boats to rest for two hours at room temperature. When you are ready to bake, preheat the oven to 350 degrees Fahrenheit Beat the egg yolk with the milk and paint the tops of the boats with this. Bake the navettes for 18 to 20 minutes or until golden on top.