"Only water to drink, thank you."
Translation:K pití jen vodu, děkuji.
In this case yes, it is wrong, unless you use a particalur strong intonation for your request and a small pause before "k pití". "Jen vodu (k pití), děkuji" making the "k pití" clearly and inserted and additional part of the sentence.
This is the answer to the (perhaps implied) question what you want to drink.
If you say you want "vodu k pití" with normal intonation and no pause, it sounds you want "water to drink" (but here closer in meaning to "drinking water"/"pitnou vodu") not that water is what you want to drink.