Avinash,
Many factors could be affecting your father's situation. Please be certain, given his age, that his prostate health is also being monitored. Being on a high liquid diet can certainly affect the bladder. Some of the mediacations he is taking could contribute to this situation. Sleeping soundly because of the Restly is another factor. There are several medications to help with bladder control. Do not be shy in discusing this with his medical team. It is probably a 'minor" problem which they wont ask about but which can be easily controlled.

Congratulations on your constant vigilance on his behalf. He is certainly fortunate to have you as an advocate.