The NH for my MIL provided a measured jug of the required fluid for the day, and MIL knew she was supposed to get through it. It did help more than just saying 'you have to drink'.
Jello also works. These help to avoid the need for IV fluids, and dehydration causes problems (falling, UTI,s etc.) It can also be a sign of nearing the end of life, along with not eating.
Fluids don't have to be liquids in order to hydrate.