Is it permissible to drink water after the second call to prayer (adhan) for Fajr in Ramadan, knowing that the questioner has been accustomed to doing so for years and intended to fast after the adhan?

If the muezzin calls the adhan at the entry of Fajr time, it is not permissible for the fasting person to drink after the adhan has begun, due to Allah's saying: "{... and eat and drink until the white thread of dawn becomes distinct to you from the black thread [of night]. Then complete the fast until the night...}" (Quran 2:187). However, if the adhan is before the entry of Fajr, there is no harm in eating and drinking until the dawn appears. Some scholars permitted eating or drinking for about a minute or so if the muezzin calls the adhan based on a calendar.

It is obligatory to intend to fast from the night before Fajr. Whoever does not intend before Fajr, their fast is not valid, and they must make it up. Making up the fast is also obligatory if the muezzin calls the adhan at the entry of Fajr, and ignorance is not an excuse in this case. If you do not know the number of days you must make up, you must make up what you are certain of or what you predominantly believe will absolve you of responsibility.