then you would recognize that your government sees the future supply of water an issue. go look up the info on the epa and other US fed gov sites. Look up the discussions on the costs of various water supply issues. Desalination, more dams (where you are getting prett built out), etc cost a heck of a lot more than being able to purchase water from canada in a "free market".
Canada is fighting states that are in the great lakes watershed from withdrawing too much water and from water from the great lakes being pumped elsewhere in the US. Why? because the US would draw more water than the system fills with, depleating the resource.