Add the water (or cream/milk) to a small bowl and then add your cracked fresh egg.

Quickly and thoroughly, whip the egg and water together using a fork or whisk until it is completely blended.

Using a basting brush, immediately apply a think layer of egg wash to any rolls or pastry dough that is ready to bake.  Be sure the egg wash is wet - don't let it dry before adding the pastry to the oven.

Don't keep the egg wash.  Just throw away any unused portions.