Declension of вода.
Nouns such as вода, чай, сахар, масло, вино, металл etc are normally used in the Singular only.
In the Plural, these nouns have the different meaning:
во́ды - various kinds of water
мета́ллы - various kinds of metal
etc
Я люблю воду́. (Singular, Accusative)
Я люблю пить воду́. (Singular, Accusative)
You should also note, that Russian has the Partitive Case, which is rarely mentioned in textbooks:
бутылка воды́. (Singular, Partitive)
Принесите воды́, пожалуйста. (Singular, Partitive)
Можно мне, пожалуйста, воды́. (Singular, Partitive)
Partitive is used instead of Genitive or Accusative, when we speak about some limited amount of X, not about all the X on the planet. Partitive looks like Genitive for most nouns. For some nouns, Partitive looks like Dative:
налить чаю
стакан сахару