Place the milk, water, and salt into a large, heavy-bottomed pot over medium-high heat and bring to a boil. Once the milk mixture comes to a boil, gradually add the cornmeal while continually whisking. Once all of the cornmeal has been incorporated, decrease the heat to low and cover. Remove lid and whisk frequently, every 3 to 4 minutes, to prevent grits from sticking or forming lumps; make sure to get into corners of pot when whisking. Cook for 20 to 25 minutes or until mixture is creamy.