Is it just me or is the suffix of 'vand' not pronounced. I did this as a listening exercise and I thought it was 'Jeg drikker vand' which makes total sense and so it isn't a case that I should have known it was 'the water' because just using 'water' wouldn't make sense.
How do I know if it is vand or vandet?
As a native Danish speaker, I can hear the -et at the end. It is very soft, and as a general rule, -t at the end of a word is rarely ever actually pronounced like a t, but more like a softer version of the English th sound. Your ears probably just need to get used to the new sounds of the Danish language ;)