"Wanakunywa"

Translation: They drink

[DiegoJaviUnlam]

Can be also "wananywa" (for progressive)?

(a conjugation chart of -nywa is below)

-nywa (infinitive kunywa)

1) to drink

From Wiktionary: https://en.wiktionary.org/wiki/nywa

[Pampelius]

I think it gets the ku- because -nywa is one syllable, so wananywa would be wrong (someone correct me if I'm wrong)

[DiegoJaviUnlam]

I still do not know if it exists a rule about it, but I have also seen more examples rejected, and I do not know if these can be alternative conjugations. For example, I have used some from the conjugation chart of -enda, and Duolingo shows some different ("ninaenda" instead of "ninakwenda", or "anaenda" instead of "anakwenda"):

https://en.wiktionary.org/wiki/enda

Edit: I think yes, here is a rule!

Polysyllabic verb that behaves as a monosyllabic verb, i.e., retains affix ku- in several tenses

Thanks for your response! :)