I think broadly speaking, yes. Forgive a misinterpretation here as I am unfamiliar with Finnish and only have a cursory knowledge of German, but it seems to me that there is a confusion here between the morphological construction of vettä (which may have some kind of semantic weight, I'm still not entirely sure as I haven't done much reading on the partitive), and the syntactic role of vettä in the sentence
In this case, the word vettä is taking the inflections typical of a noun in the partitive. However, when analyzing the sentence, it is clear that vettä is the direct object (or patient). There is a mismatch between these two ideas, but we see mismatches like this in languages all the time.
In Chukchi, a Chukotko-Kamchatkan language spoken in northeast Siberia, there is no dedicated inflection for the ergative outside of pronouns. When in situations that would call for the ergative, most nouns take the instrumental case. For example, take the sentence
ətɬəɣe ekkin waɬə pənenin. (The father sharpened the son's knife)
I haven't bothered with a gloss because the verb is very complex, but the point is ətɬəɣe, father, has taken the instrumental case ending -e. Proper nouns such as names would take the locative case, so if we were to replace ətɬəɣ- with Rintə- (a name), it would be
Rintəne ekkin waɬə pənenin.
So in Chukchi, as in Finnish, different morphological cases (that is to say, the patterns nouns can take) are used for the same syntactic case (that is to say, the function of the noun in the sentence), and in both situations there is mismatch between morphological and syntactic case. The paper I've cited below (Spencer, 2006) goes into more detail about this and provides two more examples.
Ultimately, the reasoning behind this is the fact that most of the language we use to talk about grammatical categories is based off of old grammars of Latin and Greek, two languages where morphological case and syntactic case are effectively the same thing. It never occurred to these grammarians that these two concepts aren't necessarily always linked together, and it is useful in modern linguistics to understand how they differ from one another.
In regard to vettä, I would say it is in the partitive, rather than a supposed partitive-accusative or something of that kind.
Spencer, A., 2006. Syntactic vs. morphological case. Case, valency and transitivity, 77, p.3. Link
Vinyar, A.I., Kazakova, P.N. and Naletova, P.R., 2017. Chukchi Denominal Verb Construction: Overview and Relation to Noun Incorporation. Higher School of Economics Research Paper No. WP BRP, 58. Link