It is bad luck for whomever you are making a toast if you drink from a cup containing water.
Barry explained to me that it is considered bad luck for someone if you raise your glass filled with water to make a toast on their behalf. He said that, traditionally, toasts are made using some sort of alcoholic beverage, such as champagne, wine, or a mixed drink. However, he said that it is perfectly fine for children or those opposed to alcohol to toast using some sort of a soft drink. The one thing that is not considered good etiquette is to raise a glass filled with water, as many view it as bad luck that you are wishing upon the guest of honor.
Barry remembers learning this superstition from his grandfather at a wedding he attended for his cousin when he was approximately age twelve. A toast was being made so Barry, being the minor that he was, raised his glass of water in honor of the guest. His grandfather scolded him for the action as he said it was rude and improper to do such a thing.
Barry said he did not know where the reasoning comes from to support this superstition. He continued to explain that this, like many superstitions, could have roots stemming back hundreds of years that help clarify the reason this superstition exists.
Doing some research after the interview, I discovered that this superstition comes from the United States of Americas Navy. The reasoning they use to support this superstition is that toasting with a glass of water is essentially dooming the person to be honored to a watery grave. Now after knowing this it is much more understandable. People in the navy spend large amounts of time on the water, so it would be bad to toast with something that could end one of their lives at any moment. I have not been able to ask Barry since the interview if his grandfather was in the Navy or not.
I found this superstition at:
http://en.wikipedia.org/wiki/Toast_%28honor%29#Beverage_choice