The use of water in a slow cooker depends on the recipe and the cooking method you are employing. In many cases, you may need to add some liquid, but it doesn't necessarily have to be water. Here are some scenarios:
Traditional slow cooking: If you are cooking a roast, stew, or any dish with substantial ingredients, you'll likely want to add some liquid to ensure the food doesn't dry out. Water can be used, but you might also consider using broth, stock, wine, or even canned tomatoes for added flavor.
Moisture-rich ingredients: Certain ingredients release a lot of moisture while cooking, like vegetables or meat with high water content (e.g., chicken). In these cases, you might not need to add any extra liquid as they will create their own.
Recipes that don't require much liquid: Some recipes, like certain sauces or desserts, may not require much added liquid, as they are meant to thicken and intensify in flavor.
Layered cooking: In some cases, if you have a base layer of sturdy vegetables (e.g., potatoes, carrots) under your meat, they can release enough moisture on their own to cook the dish.
Steaming vs. stewing: If you're using the slow cooker as a steamer (e.g., cooking fish or vegetables), you might not need any liquid, as the food will cook through the steam generated.
In summary, the decision to add water or other liquids to the slow cooker depends on the specific recipe you are following and the ingredients used. Always check the recipe instructions for guidance on the amount and type of liquid required. Generally, adding some liquid is a good idea to prevent the food from drying out during the extended cooking process.