Depends on how you define "consumption". If you include agricultural and industrial use, then a lot comes from aquifers. An no those aren't used in short, local

Depends on how you define "consumption". If you include agricultural and industrial use, then a lot comes from aquifers. An no those aren't used in short, local cycles; a lot of (polluted) water is moved overland (in rivers) to locations and distributed far and wide. I don't have any numbers at hand on sources of domestic consumption for major cities across the world, but I do know that most cities in Europe rely on a combination of surface and aquifer water to fill their treatment plants and supply systems. When you open the tap, it's not the same water you flushed down the drain when you showered last week. (I've worked on water modeling but not on a fine enough scale to be able to remember an exact answer to your question). But, when talking 'water shortage', the image the media paints is inaccurate. The California water shortages are not a (representative) example of the long term problems. A more realistic (but abstract, which is why it doesn't make a nice story in the newspaper...) scenario is that of drought in less developed countries. Climate change makes summer hotter and monsoons more intense. Land is degraded due to lack of planting when plants die off in summer heat. Rain in winter then flushes away because there is nothing to hold to water (soil erosion). Crops fail, war erupts. Wars in Africa or Asia influence the rest of the world as well, but yeah that's not the same story as 'water shortage! Your tap in California will stop working!'. And if Africa or Asia are too abstract - southern Europe faces the same problems, albeit in a less severe form (and with better options to control). In the aggregate, what you say can be said of any resource. "We don't have an oil problem, just the energy problem of converting airborne carbon into a liquid combustible form." When I put it like that, it's obviously a ridiculous reduction; and while the water issue isn't prima facie ridiculous when phrased like you do, the underlying dynamic is the same. It's true that we have no less water than 10k years ago; but it's in different places, is put on land through different forces, is contaminated with other chemicals making it unsuitable for direct use.