The Great Lakes hold about 21 percent of the planet's surface fresh water, yet less than one percent of that volume renews each year. That second number, not the first, sets the limits on everyone who drinks from the basin.
With 1% of renewal every year, in a dynamic equilibrium, the average water will be 100 years old. Some parts might be older some parts might be younger. But on average it will be 100 years old.
With 1% of renewal every year, in a dynamic equilibrium, the average water will be 100 years old. Some parts might be older some parts might be younger. But on average it will be 100 years old.