With no direct words for "water", you can describe where it's from in the context of where and when you use it. Helper words here are ofaal (receive) naak (eat) kip (food). Examples : "I drank river water with my food" which can be translated as "Zu'u ofaal osos rath voth dii kip". You can use "Zu'u ofaal nol fin rath" (I received from the river) or you can specify "into the mouth" -> "Zu'u ofaal rath kotin dii jot" or "Zu'u naak nol rath" (I ate/drank from the river). You can use further context in how you use the sentence to make it clearer:

They sat by the river and drank water -> They sat by the river and drank from it -> Nust praal ahst fin rath ahrk ofaal / kip nol nii. It can arguably be implied that both eating and drinking happened from the river.