The Civilization Record
Water
The amount of water on Earth has barely changed across the whole of human history. About 1.386 billion km³ of water moves in a constant cycle through oceans, glaciers, groundwater, lakes and the atmosphere.
What changed is how much water humanity draws from that cycle. With the start of farming, people stepped outside a life dependent on rainfall and began to direct water with canals, wells and irrigation systems. As cities and industry grew, so did withdrawals for drinking water, production and energy.
Today humanity withdraws about 4,100 km³ of fresh water a year. About 70% of it is used in agriculture. Groundwater is a significant part of this use, and in some regions the water withdrawn is consumed faster than it naturally refills.
Water is therefore not only a resource but a continually renewed flow on which civilisation is built. While the planet's water stays fixed, humanity's share of that flow and its capacity to direct it have grown.
Worth knowing
Humans appropriate about half of accessible runoff.
Virtual water in trade: importing water-intensive goods effectively moves water from wet regions to dry ones.
The Aral Sea has lost most of its volume to irrigation withdrawal since 1960, a scale marker.
Agriculture takes 70% of global freshwater withdrawal; industry 19%, municipal 11%.