Why is it bad luck to toast with water?

Answer 1

In Greek mythology the dead are believed to forget their corporeal lives after drinking from one of the rivers leading to the underworld.

It is customary to toast the dead with water, symbolising this voyage to the underworld, and when making other toasts if they are made with water it is seen as wishing bad luck, or even death, on that being toasted.

Answer 2

Yes, it may cause a cosmic reaction that influences sailors: possibly throwing one overboard or worse!