Why is it воды is this sentence but вода in others?
"Нет" requires that the noun it modifies be in the genitive case. The singular genitive case of "Вода" is "Воды".
У меня нет водЫ
I just realized we aren't using есть when writing negative statements of "to have". Is that a rule? Thanks.
Yes, it would be a mistake putting «есть» when you already have «нет». Think of «нет» as “there is/are not” in one word.
No genitive singular for меня?
That is genitive (and accusative) singular of Я.
Look at "bernibuds" explanation in a previous answer: вода - воды
Is there anything wrong with translating sentences of this form as "I have no water", "He has no apples", etc? Duolingo is very hit-and-miss about that form, accepting it for some sentences but not for others with no discernable pattern.
How do we write water in Cyrillic? I tried водй but it says there is a spelling error. Thanks.
The genitive singular (used in this sentence) is "Воды". Do you have Cyrillic activated in this course?
It accepts answers written in Cyrillic even if you have the transliteration on.
Why is меня used, rather than я?
"У" is followed by the genitive case - in this case the genitive of "я", which is "меня".
why is У меня нет вода wrong?
Вода must be in genitive case, as you're expressing the absence of water with нет. Words ending in -a/-я in Russian typically take the -и/-ы ending in genitive singular, so вода becomes воды.