Preheat oven to 250℉. Line an extra-large sheet pan (or 2 smaller sheet pans) with parchment paper or a silicone baking mat and set aside.
In a very large bowl, whisk egg whites, vanilla, and water until frothy. Toss walnuts in egg white mixture until well coated.
Add granulated sugar, brown sugar, cinnamon, and salt to the egg and walnut mixture. Stir gently to coat all walnuts until well covered. Spread coated walnuts in a single layer across a baking sheet. Make sure nuts are not overlapping.
Bake in preheated oven for 1 hour, flipping and stirring walnuts every 15 minutes. Allow walnuts to stand for 30–60 minutes to fully cool and solidify.
Video
Notes
Nutrition: The nutrition information is calculated for a 1-ounce serving.Storage: Keep at room temperature for 2 weeks. For longer storage, place in a sealed, airtight container in a cool, dark area for up to a month. Alternatively, freeze in an airtight container for up to 2 months. When thawing, remove from the bag and let sit at room temperature to prevent softening or stickiness.