answer:Drinking water or soda will have no affect (nor will the salt) on the cough syrup’s effectiveness. Here is how the two types work: “suppress or expectorate coughs. Cough suppressants prevent coughs by temporarily drying out the mucous membranes. Cough suppressants include Codeine, Hydrocodone, Noscapine, Acetylmorphone and Pholcodine. Expectorants do just the opposite of suppressants. If a patient is complaining of congestion, he or she may be given an expectorant to loosen the phlegm in order to expel it from the body.” Source