Called fargo water treatment, they built a RO facility like 5 years ago. Guy I spoke with said the percentage they use varies depending on demand but during off peak seasons, they can supply the majority of fargos water as RO. He said the capability of the plant is about 18m gallons / day and use is often around 20 to 22 milllion gallons / day.
Not all water treatment plants have the same design criteria even though they have roughly the same end goal for water quality. Since the Canadians and Minnetuckians have proven their willingness to sue ND and the federal government, this project would get stuck in the courts and environmental studies for decades.
So, let's say for the pure fun of it that ND and the federal government would agree to "treat" the water coming through the Tolna Coulee to satisfy the environmentalists and foreign interests (yes, Minnetucky is included in that for me). One would need to treat roughly 2,000 cfs (I vaguely remember that was the number tossed around as an input to DL).
2,000 cfs coming out of there would have to be RO'd for chemistry reasons, but you'd also have to install a water treatment plant similar to what is going in for NAWS to remove biota. Hey, I don't make the rules here, but that's what the courts and those who sued over the Red RIver Valley Water Supply and NAWS projects have sought and largely won through the courts and concessions made by ND and our federal government.
Anyway, 2,000 cfs equals 1,292,630,400 gallons of water per day. So, you would need a water treatment plant roughly 65 times the size of the Fargo one and it would also have to remove biota to the nine 9's according to Canada.
Oh yeah, and that doesn't deliver a single drop of drinking water. That's just what would be expected to happen if water were to come out of the east end of DL.
Before one gets all high and mighty and says the hell with Canada, the above is based on treaties with Canada and we need to remember that ratified treaties are considered the law of the land.
One should also remember that the whole idea behind this thread was one of not allowing your drain to affect your neighbor. Dumping fresh water onto someone else is one thing, dumping undrinkable and environment altering saline water is a whole 'nother thing.