By the way, regarding the stress-shifts in вода -- quite a few other common feminine nouns, such as рука (hand/arm), нога (foot/leg), and голова (head) follow a rather similar pattern of stress shifts, though unfortunately the pattern is not always exactly identical throughout the entire declension. For instance:

Nom. sg. вода, рука, нога, голова
Gen. sg. воды, руки, ноги, головы
Acc. sg. воду, руку, ногу, голову
Nom./Acc. pl. воды, руки, ноги, головы
Gen. pl. вод, рук, ног, голов
Dat. pl. рукам, ногам, головам (BUT водам, not водам)

In the singular, all these nouns behave identically (stress on the ending except in the accusative, where it shifts to the first syllable), while in the nominative plural, the stress also shifts to the first syllable -- thus distinguishing it in pronunciation from the genitive singular, though the nom. pl. and gen. sg. have the same spellings. However, "water" breaks the pattern a bit in the dative, instrumental, and prepositional plurals.

Anyway, I wouldn't fret about totally memorizing the individual declensions of all these nouns right away; just be aware that the stress-shift you see in nom.sg. вода and acc. sg. воду is a pattern you're going to see again!