Newborn kittens should not be fed water. Newborn kittens need mother's milk or kitten milk replacer. Kitten milk replacer can be purchased at pet stores or veterinary clinics if the mother has abandoned her kittens. Do NOT feed cow's milk; this does not have the appropriate nutrient requirements and leads to gastrointestinal upset. You will also need to stimulate newborn kittens to urinate and defecate. This is done by rubbing a warm, wet cotton ball over the hind end after eating; usually the mother does this during grooming.
You can give it to them anytime, but their eyes should be open. Just go to the pet store and buy the formula and bottle.