"I want chili pepper water."
Translation:Makemake au i ke kai nīoi.
Kai nīoi is the standard term among native speakers. This is probably because for wai huaʻai, the juice (wai) actually comes from squeezing the fruit (huaʻai), but for kai nīoi, it's a sauce or broth (kai) made with chili peppers (nīoi) as the main ingredient.
Additional confusion for speakers of English is probably that in English we call it "chili pepper water," since water is another main ingredient, usually along with Hawaiian salt and vinegar, but the latter ingredients are not so visible as the water. When you look at a bottle of chili pepper water, you generally only see the chili peppers and the water. But ʻono!
This is also a good time to point out that "wai" has many, many meanings beside just "water." As we just saw in the above example, one meaning is "juice." Check it out in the Pukui dictionary or on the web.
And might as well comment on an earlier question (a year ago) from CATipton on this same page: You could say Makemake au i kai nīoi (without the "ke"), but it would be best translated as "I want SOME chili pepper water." That's grammatically correct but has a slightly different meaning.