Preheat an oven to 180 degrees C. Mix the crackers and melted butter together in a bowl; set aside.
Bring water and chicken stock to a boil in a saucepan over high heat. Season with salt and black pepper. Add the chicken. Reduce heat to a simmer then cook, stirring occasionally, until chicken is no longer pink in the centre, 5 to 7 minutes. Drain the chicken; set aside. Whisk together the sour cream and cream of chicken soup in a large bowl. Stir in the chicken then transfer the mixture to a baking dish. Sprinkle the cracker mixture on top.
Bake in the preheated oven until bubbly, 25 to 30 minutes.
If making for the first time add half of the sour cream and taste first. Add more if desired, tasting as you go, to reach desired flavour. Serve over cooked white rice.