Why should people tolerate the seizure of their water by the water magnate?
Why should they leave, just because he seizes the water?
By what mechanism is it just he does so?
Seizure of natural resources, such as water, or by logging, has either to be modulated to make it just, and not monopolizable, or recognized as criminal corruption.
If the resources were not in use by anyone, then it is just for him to appropriate it. For example, if there was a flowing river that people drank from, it would not be just for him to claim this resource. If the river was polluted and he built a plant that purified the water, it would definitely be just for him to be the sole owner of that purified water. How could it not be? If he digs a well and draws water from it, who else is owner of that water?
Now if people rely on the water from his well as there is no other source of water there, then they still do not have the right to steal from him this water if they otherwise die. It is his water by right of appropriation and no one else's. He mixed his labor with nature and created value that he owns, and it is his to distribute.
It is preposterous to suppose a sole individual constructing such a facility alone, on their own dime. This is a straw man argument.
Corporations do this kind of construction, and they demonstrably and unfairly gain such resources despite other's use of them routinely, and characteristically.
That water is part of a water table, which isn't separate from the water in the surrounding area. Various communities try to regulate this commons, and are routinely and characteristically corrupted by corporations to favor them.
This is preposterous as well. What prevents me from appropriating the air you need to breathe, then? If I build a box around you, and prevent air from being exchanged within it, according to you I have done nothing wrong.
That is exactly the same argument as someone digging a well that then deprives others' use of water in other parts of the water table - and this is the extant state of government.