Even if it were owned by a group of 100 people, if all had the right to use as much as they want and it will eventually be used up, the incentives for such a resource make it a tragedy of the commons.
It would be better if all the existing users or all the residents of the region became shareholders in a corporation that charged everybody for what they use. Owners have an incentive to not let their resource be all used up at low prices. No, they want to conserve a resource and charge higher prices if they can.
The everybody-owns-it model means people only pay for the cost of pumping the water, without any regard for what water will cost once the resource is gone. A resource with sensible ownership, on the other hand, would incentivize conservation, because customers are more likely to pay a price that reflects the future value of the water, not just the cost to pump it.
So, no, I don't think the current situation is capitalism. It is a situation that property rights has not been properly applied to yet.