"The cows drink cold water."
Translation:De koeien drinken koud water.
Because "water" is a het word, which means you don't add the -e ending to the adjective. You're right - most of the time -e is added, but the two exceptions are, 1) When it comes before a het-word with no article (like this sentence) , and 2) When it comes before a het-word with the article "een". Make sense?