I had the better position and plenty of time on my clock.
My opponent had less then 10 minutes on his clock.
I also taken a couple of bathroom breaks.
He opened his bottle and started to drink it.
About 10 minutes after drinking the water, my opponent needed to use the bathroom which he did.
While he was gone from the board, he went over on the clock.
I may misunderstand the chronology - It does not quite seem to tally as if taken at face value he would have drunk the water at or after the end of his available time. However, taking that to mean that he was within a few minutes of his time expiring, it sounds like him drinking and then taking a toilet break were within a few minutes of each other and very close indeed to his time expiry.
No rational person would abandon a situation that was critical to them instead of waiting a few more minutes even under extreme duress. It is also very likely that a highly dehydrated person will also have a full bladder.
I above said " ... no rational person ...". It seems likely that the person was either acting irrationally (which is quite possible in such circumstances) or was effectively resigning. You could not reasonably expect such behaviour as a response to your action.
- At "best" you might expect to gain a few seconds from their opening the drink.
- Distraction per se is a possibility but probably a rather extreme gambit.
- It is also likely that the water would improve their ability to play better in the closing moments.
- It seems almost unthinkable that giving them water at that stage would have initiated a 'toilet break'.
Overall you action seems on balance to have been neutral or to have improved their (slim) chances. To we as onlookers your actions seem ethically proper.
It seems worth adding, and only you know this one way or the other, that it MAY be that your intentions were in fact calculated to add to your advantage and that you still remember this long after. Even if this was the case, it seems a ploy more liable to fail than succeed and the actual degree of its success would be very unexpected.
An aside - which may actually help: I'm getting 'oldish'. On occasions I wake in the wee small hours with memories of events from decades or many decades past where I recall & mentally run through past actions and wonder if I did things as well as I could. I am generally seen as "an honest & upright" person - and that is my aim in life. It doesn't seem to stop my brain questioning my past motives and deeds :-)