Add in the water and vanilla extract. Mix until incorporated into the sugar mixture.
In a separate bowl, combine the dry ingredients.
Add the dry of the ingredients to the sugar mixture and mix together until they are all well combined.
Divide the dough in half and form two large balls. Wrap tightly with plastic wrap and place them in the fridge to cool for at least 1 hour. (You can also make this at night and allow to sit overnight.)
Preheat oven to 350° F
Line baking sheet with parchment paper.
Remove the chilled dough balls from the refrigerator.
Begin shaping balls using roughly 2 tsps. of dough for each ball. The balls should be slighly smaller than a walnut in the shell. Place them about ½″ apart on a baking sheet.
Bake for 15-18 minutes, or until golden brown on the bottom, the tops will be a very pale golden brown.
Let them cool on the baking sheet for about 5 minutes.
While they are cooling, make the powdering mixture by thoroughly combing the powdered sugar and potato starch.
Once the cookies are cooled (they'll still be slightly warm), gently roll them in the powdered sugar mixture.
Dust with powdered sugar right before serving, if desired.
Recipe by Marine Corps Nomads at https://marinecorpsnomads.com/2012/12/gluten-free-snowball-cookies.html