"Matěj potřebuje vodu."

Translation: Matěj needs water.

[imaldastar]

what is the difference between voda/vodu? and kava/kavu?

[VladaFu]

One is nominative, the other is accusative. Czech nouns use grammatical cases, check the lecture notes.

[Nides14]

This says almost the same as "Matěj má velká žizeň", doesn't it?

[VladaFu]

Firstly, velkou žízeň. Secondly, no-one said what does he need it for.

[Nides14]

Oh, so need doesn't stand for a need to consume only

[VladaFu]

Here we have just "Matěj needs water.". It could be for anything. Washing something, extinguishing a fire, diluting something etc.