[ephbit]

True. Not that big.

But let's not forget that it's not about merely pumping the water around. All this water must be processed. And I figure the process is a little more involved than simple reverse osmosis for seawater desalination.

In the desalination business 1 m diameter pipes with water traveling at 1 m/s and the resulting volumetric flow rate isn't a big thing .. but I'd guess for more complex processes it indicates huge/expensive apparatuses.