I disagree, humanity has always found a way. Scientists and engineers will find ways to purify water for drinking and other uses, such as desalination. Sure, we will experience a crisis and possibly global panic, but we'll make it out alive. The political charade of "everything's fine, man made climate change isn't real" will only last so long as the everyday person doesn't have to directly experience the consequences. Then we'll start to see change.
One could argue that the treatment would be unnatural and could potentially have unknown side effects if the patient were to survive. I would accept anything if it could extend my life. But not if I knew I wouldn't be able to live an enjoyable quality of life afterwards. I suppose only time will tell, that is if such an injection were to ever enter real world applications.