Sift together the powdered sugar, merengue powder and salt in a mixing bowl.
In a stand mixer, add the paddle attachment and start mixing the dry ingredients slowly.
Slowly pour about 1/2 cup of water first and let it mix for 3 minutes on medium to high speed.
Stop the mixer and scrap down the sides of the bowl.
Add the pure vanilla extract and continue to mix for another 5 minutes on medium to low speed.
You will see that the mixture will start to thicken.
If you like the consistency, stop the machine, and cover the icing immediatly to avoid having the royal icing dry up on you.
Note: If you see that the consistency it too thick, add more water a tablespoon at a time. Do not water down the mixture for once it is too wet, the consistency will be too runny to use as outlines for cookies or decorating.