This paper offers a technical and geopolitical reappraisal of a macroengineering proposal to plumb Earth’s freshwater, siphoning some of it from a region of surplus (Amazon River Basin) to a region of shortage (arid northern Africa) via ...(a) Transatlantic Freshwater Aqueduct. Two different routes for the pipeline, of length 4,317 and 3,745 km, respectively, have been considered. Pipe diameters larger than 60 m are necessary for “reasonable” low pumping power (i.e., less than 20 GW). ... To keep the number of pumping stations reasonably small (i.e. fewer than 20) a single pipe of diameter higher than 30 m (or bundles of smaller diameter pipes) is required. The Atlantic Ocean currents may be used to provide the necessary power for pumps. ... A rough cost estimate of the project is about 20,600 GUSD and 18,400 GUSD, respectively, for two pipeline routes.Their cost estimates are based on the now-defunct Alaska-California proposal. I do not know what a GUSD is but I suspect it's a lot of money.
Bottom Line: Build it soon while it's still cheap.