У девочки нет воды.
Short, and simple:
Why's the "а" replaced with "и" rather than "ы"?
Forming the genitive case
1. If the noun ends in a consonant, add “а”.
2. Replace “й”, with “я”.
3. Replace “ь”, add “я”.
1. Replace “а” with “ы”.
2. Replace “я” with “и”.
3. Replace “ь” with “и”.
1. Replace “о” with “а”
*2. Replace “е” with “я” *
in Russian, after к there is never ы, so in the genitive you replace the а with и instead
This is one of the Russian spelling rules - in this case rule #1. It is essential you learn these, the earlier the better.
Added: Have you been reading the Tips and Notes for the Russian course as you go? Your question was answered in the Tips and Notes for the "Animals-1" skill, which you just completed:
There are some restrictions on which consonants are used with which vowels when making word forms. Here are the rules for и, а, у vs. ы, я, ю:
use only И, not Ы, after к, г, х/ ж, ш, щ, ч
Yeah, I even memorized those rules, when I was learning plurals!
Alright, it makes a lot more sense now, the reason was also obvious.
Thanks for the reminder!
This is the forum for Duolingo in English. Your helpful tips may last longer and be of much more benefit in the Russian forum. IF you want to leave it here, may be change the title to an English one to help people find it.
That was my initial intention, I don't understand why it was posted in DUO English.