"The girl has no water."
Translation:У девочки нет воды.
At this point I imagine this to be the conversation of Duoling zoo workers... they have all these cages everywhere with men, women, children, girls and boys, dogs, horses and weirder stuff... And they keep reminding each other: "Look, the girl didn't get her daily dose of apples and bread yet." "The horses have no water!"
У (genitive) нет (genitive)
У девочка(-а+ы-ы+и) нет вода(-а+ы)
У девочки нет воды
http://www.russianlessons.net/grammar/spelling_rules.php (Spelling Rule 1: Ы - И)
I am no expert, but I got this: When you are talking about something that the subject owns (like "the girl has a book"), you use есть When you are talking about something the subject lacks (like in this case, "the girl has no water", or "the girl does not have water"), you use нет. I hope it was of help!