The idea is for this petition to stop it before it passes. That way individual countries could not make that decision.
I am not sure but if this petition stops this legislation and declares water a basic human right, then no country would be able to privatize water. And if one did it could be considered to be commiting "crimes against humanity" or something similar? So they could be forced to revoke their decision, be heavily penalized, or even attacked by the EU/UN or other organization?
I am not sure about this part because the video and the information on the web do not go into detail about the consequences if this is approved. But even in a worst case scenario, where this legislation could allow military action, I feel it would be justified as for me this really could be just as bad as slavery, dictatorship, tyranny, or even massacre.