Is it necessary/obligatory to drink the Zam Zam water in standing position? What should we say when meet the man/woman at first time after he/she returned performing Haj/Umra?

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.

It is not obligatory to drink Zamzam water in a standing position. The fact that the Prophet, sallallaahu ‘alayhi wa sallam, drank Zamzam water while he was standing was to indicate that it is permissible to do so if needed and not that it is obligatory. It has been narrated on the authority of Ash-Sha‘bi that Ibn ‘Abbaas reported that the Prophet, sallallaahu ‘alayhi wa sallam, drank (water) from Zamzam from a bucket while he was standing. [Muslim]

In another narration, Ibn ‘Abbaas said, "The Prophet, sallallaahu ‘alayhi wa sallam, drank while standing from Zamzam." [Al-Bukhari]

Meanwhile, drinking while standing was forbidden in the Hadeeth reported by Abu Sa‘eed Al-Khudri that the Messenger of Allaah, sallallaahu ‘alayhi wa sallam, forbade drinking while standing. [Muslim] Imaam An-Nawawi commented on this Hadeeth, saying: "The forbiddance (mentioned in the Hadeeth) is to be understood as reprehensibleness (not prohibited). And the fact that he, sallallaahu ‘alayhi wa sallam, drank while standing indicates that it is permissible to do so. Hence, there is no contradiction in this regard." [Explanation of Saheeh Muslim]

For more benefit, please refer to Fatwa 83276.

As far as we know, there is no reported statement or expression to be said to the person upon returning from Hajj or ‘Umrah; however, there is no harm in welcoming and congratulating him with a customary permissible expressions such as "May Allaah accept your Hajj" or "Praise Allaah that you have returned safe and sound," or "Praise Allaah for reuniting us," or similar expressions that indicate happiness with one's safe return.

Al-Qayloobi said in his annotations to the commentary of (An-Nawawi's) Minhaaj (At-Taalibeen): "It is recommended for the man to take his family with him to Hajj and to take gifts with him and to to bring gifts for them (his family) when he returns from any trip, even if it is a short one. It is also recommended for him to send a messenger informing his family that he is arriving soon. It is not recommended for him to drop by at night; he should first go to the nearest mosque and perform two Rak‘ahs as a Sunnah prayer upon arrival from travel. It is recommended to throw a banquet, known as Al-Naqee‘ah, for the traveler when he returns home, and his family should be at his reception with others. When someone comes back from Hajj or ‘Umrah, it is recommended to congratulate him by saying, 'May Allaah accept your Hajj or ‘Umrah, forgive your sins, and compensate you for what you spent.' If the person returns from a military expedition, it may be said to him, 'Praise Allaah for blessing you with victory and honor.'"

As-Subki said: "The Companions of the Messenger of Allaah, sallallaahu ‘alayhi wa sallam, used to embrace one another when returning from travel. ‘Aa'ishah reported that Zayd ibn Haarithah arrived in Madeenah while the Messenger of Allaah, sallallaahu ‘alayhi wa sallam, was in her house. Zayd knocked on the door and the Prophet, sallallaahu ‘alayhi wa sallam, rose to welcome him, trailing his garment. He embraced and kissed him." [At-Tirmithi: Hasan (good)]

Allaah Knows best.