As far as following every directive of prophet Muhammad (SWS) is concerned, yes it is obligatory upon Muslims to follow that, whether it is of a worldly nature or of a religious nature (See: Quran 49:1-5, Quran 33:36, Quran 4:65, Quran 24:63). If Prophet Muhammad (sws) had directed Muslims to do a certain thing or refrain from a certain thing at that time, then it is obligatory upon us, even today to follow that directive. There are two points that need to be addressed in this context:

1) the authentcity of the directive: If it reaches to us through Quran and Sunnah, then there is no issue of credibility because of ijma and tawatur. If however it reaches to us through akhbar-i-ahad, then first we have to establish its credibility and after establishing it, if we are satisfied, then it definitely becomes obligatory upon us to follow that directive.

2) The nature of report: Whether the narration reported is a verdict of Prophet (SWS), His ijtihad etc. or a mere advice, personal liking disliking on a certain matter etc. This disctinction is necessary because if it is from the former category, then it is obligatory but if it is from the latter category, then it does not become obligatory. The drinking of water while sitting falls in the second category and other narrations which indicate allowance for drinking water while standing themselves point to this fact that it was not a directive of Prophet Muhammad (sws). (See: Discussion 77515).

For a detailed-discussion on this topic, refer to Complete 13-Parts Discussion: Discussion 58889 • Reply 68344)

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And also following videos specifically:

Please refer to the video below from 00:42 to 14:58

Please also refer to the video below (specifically from 12:09 to 26:09)

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Please also refer to the video below from 16:29 to 23:47