Should expectorant cough syrup be taken with or without water?

Cough syrup +/-water. It is best to stay hydrated when taking an expectorant cough medication. I do not recommend cough medication to my patients. I do however prescribe guaifenesin-containing medications. When i do, i ask that they take the medication with a glass of water. Ask your pharmacist about the best way to take the specific medication prescribed for you.
Water... Most people are able to expectorate sputum without expectorant cough syrup. Increasing your water intake by itself may make the mucous thinner and thus easier to expectorate. If you smoke, quitting will lead to less mucous production.
EITHER IS FINE. You will not decrease efficacy one way or the other with normal amounts of water.