That's why there is a Canadian federal law that bans the sale of bulk water from Canada in spite of all the years lobbying from business concerns on both sides of the border.
In some published fact source it is said that Canada has the largest amount of fresh water resources on this planet. Shouldn't we share it with our thirsty southern neighbor and make easy money too? Uhuh.
The long range view is that once the export of bulk water - rivers, glaciers, icebergs - is allowed the demand from the US will be insatiable. If bulk water becomes a tradable commodity it will be very difficult to then restrict its trade without coming up against free trade principles and probably against other ingenuous interpretation of trade laws. Perhaps even leading to war and regime change as Porky realizes.
The higher price water starved American cities , industries and farms will be willing to pay will result in a even higher price of water to Canadian consumers. If enough water is diverted from Canada whole weather systems and ecosystems will be affected. America is indeed super powerful in more ways than one.
I believe there is already one clear example from the Columbia River that flows into the western US. The US has drawn so much water from this river that it is affecting its source in the Canadian Rockies and most of the salmon spawning streams have been degraded. There isn't enough water in most years for the salmon to reach their traditional spawning streams. But due to a bilateral agreement on the management of the river Canada is not allowed to do anything witout US assent, to hold back water to improve salmon spawning conditions although this will improve immensely the health of the river.
Canada does not need to divert any of that water for its own use and the amount involved is minimal and seasonal. To the Americans this "control" is the first crack by Canadians to control their source of water. The bilateral agreement turned out to be a bad deal for Canada and it was suckered because no one thought of those issues at that time. Fortunately in this instance only the salmon will suffer, mainly the American salmon fisheries at that. But it is a very poignant example to Canada about the management of water resources that the US covets. A blanket ban prevents any insidious backdoor breaches.