Your husband, or indeed any of us, will be forgetful if he is not drinking enough fluids. So, make sure he is drinking enough water in the course of the day.
Next point even with a pillbox that is clearly marked with the days of the week and morning, midday, evening and night, if he is forgetful or unwilling to take his pills you will still need to remind him, unless you prefer to get a nurse coming in to make sure he takes his medicine.
It is difficult to deal with this kind of behaviour, but he is not going to get better if he doesn't take his medicine, is he? Nor is his memory likely to improve if he is short of fluids.