nepoivatelným
Nepoivatelným is a form that appears in some Czech-language texts, but it is not a standard or widely recognized entry in modern Czech dictionaries. It is generally understood as a grammatical form of an adjective with a negative prefix, related to the idea of drinkability, but its exact meaning and acceptance vary by context. In practice, the form is uncommon and many writers would prefer more common expressions.
Nepoivatelným would be the instrumental singular masculine/neuter form of a hypothetical adjective nepoivatelný. Because this adjective
If encountered, nepoivatelným is usually interpreted as a descriptor indicating something unsuitable for drinking or unsafe
For clarity in contemporary usage, it is better to use standard negations such as nepítelný/nepitný in Czech
pitný, nepítý, nepitný, poživatelné, nepoživatelné
No major dictionary entries confirm nepoivatelným as a standard Czech form.