How to
How to give a reminder that lands
The same instruction can be followed easily or refused entirely depending on how it is worded and when it arrives.
Short answer
One step, short words, warm tone, same time every day, and never a reminder that points out the forgetting. Give the person something to do, not something they failed to do.
One thing at a time
"Have a drink and then we'll get your coat on" is two instructions and usually produces neither. Say the first, wait, then say the second.
Use the wording they use
"Time for your cuppa" beats "hydration reminder" every single time. Familiar phrases are processed faster and feel like a person rather than a system.
Never reference the forgetting
"You forgot again" and "don't forget" both point at the deficit. "Time for lunch" points at the action. The second is followed far more often and costs nothing in dignity.
Same time, same words
Repetition is what turns a prompt into a habit. Varying the wording daily makes each message new and unfamiliar, which is exactly the wrong thing.
Pick the right moment
Late afternoon is a difficult window for many people with dementia. Put important prompts in the morning where possible, and land any late-day prompt before the difficult hour, not during it.