The English sentence is a little vague, “grabbing” in this context is usually used to describe the action of "going to grab" a glass of water, and not the actually "holding" of a glass of water. Therefore unsure if the sentence is: 1. I am going to grab a glass of water OR 2. I am holding a glass of water Here's the Chinese for both scenarios: 1. 我去拿一杯水 wo3 qu4 na2 yi4 bei1 shui3 2. 我拿着一杯水 wo3 na2 zhe yi4 bei1 shui3

wo zheng na zhe yi bei shui.

you can also say it like this: wo3 zheng4 duan1 zhe yi4 bei1 shui3 我正端着一杯水 or wo3 zheng4 duan1zhe shui3 bei1 我正端着水杯

我拿着一杯水 or 我捧着一杯水 wo3 na2 zhe yi4 bei1 shui3 or wo3 peng3 zhe yi4 bei1 shui3

Wo na zhe yi bei shui