The phrase "to warm the water" means to increase the temperature of the water so it becomes hotter or more comfortable for various purposes like bathing, cooking, or drinking. Full definition
To begin, place 1 1/2 cups of warm water in a mixing bowl, with 1 tablespoon of brown sugar and 2 teaspoons of kosher salt. (cosmopolitancornbread.com)
Surface wash in warm water with mild soap and rinse thoroughly. (diaperjunction.com)
Combine the miso with 1/4 cup warm water in a small container and whisk until smooth. (vegkitchen.com)