Sprinkle a little bit of the dry onion soup mix in the bottom of the slow cooker. Put in chicken and spread mushroom soup on top. Sprinkle the rest of the onion soup on the chicken and add the water. Cook on low 4-6 hours or on high 3-5 hours.
Mix the mushroom soup and onion soup together in a small bowl. Spread a small amount of the soup mixture in the bottom of a glass 9x13 baking dish. Put the chicken in and spread the remaining soup mixture on top. Add water and bake covered at 350 degrees F for 45-60 minutes or until chicken is cooked through.