The simple answer is yes. Like any exercise, you need to keep your body hydrated. Singing is the same. Our vocal folds are being used when we sing and we also expect quite a lot of them… especially when we sing high.
A lot of people thing that hydrating the voice means just drinking as you sing but the water actually needs to get in to your system to hydrate the voice properly. This is why drinking enough water, all day long, is crucial if you use your voice a lot.
This isn’t just for singing, this also applies if you use your voice a lot. Teachers, who speak all day long, should really be drinking lots of water too. Is it sad that I actually love water? You’ll always see me with (or near) a big bottle of water.