Bring water, butter, and salt to a rolling boil in a heavy saucepan.
Add the flour all at once and cook over low heat, beating vigorously with a wooden spoon until mixture leaves the sides of pan and forms a compact ball.
Remove from heat.
Beat in eggs, one at a time.
Continue beating until mixture is smooth and has a satin sheen.
Mix in the Parmesan cheese.
Force dough through a pastry bag and tube, or drop by slightly rounded measuring teaspoonfuls 1 inch apart onto a lightly greased baking sheet.
Bake at 375°F 20 minutes, or until golden.
Remove the puffs to wire rack and cool.
When cool, cut off tops of puffs, fill as desired, and replace tops.