Answered by Mufti Yusuf Mullan
Buying and Selling Zam Zam water: is it allowed?

Wa alaikum salaam,
Buying and selling bottled zam zam water is indeed permissible. It follows the general rulings of buying and selling.
Water is essentially from the things which are free and have no owner. It is jointly owned by all people. However once a person intentionally obtains possession of water e.g. gathers it in a bottle, they become the absolute owners thereof. No other now has a right over this water. It may be sold, bought and gifted etc. It is mentioned in the Majalla al-Ahkam al-Adliyyah, the great Ottoman codification of Hanafi commercial and trade law:
1249. Any person who obtains possession of a thing which is free, becomes the independent owner thereof. Example:- A, by means of a receptacle such as a jug or a can obtains water from a river and stores it therein. The water becomes the property of A. No other person may make use of it without A’s permission. If any other person takes and consumes it without A’s permission, he must make good the loss.
1250. Taking possession must be coupled with intention. Consequently, if any person puts out a receptacle with the object of catching rain water, the rain water caught in the receptacle becomes that person’s property. Again, water is collected in a receptacle not intentionally put in any particular place, does not become the property of the owner thereof. Any other person may take it and consume it.
And Allah knows best.