Throughout history, societies have sought to alter the behaviour and availability of hydrological systems. Early water supply systems involved the building of dams to provide a constant water supply over changing seasons, and aqueducts to facilitate the movement of water to areas with limited supply. Early irrigation systems involved the building of hillside terraces, which used gravity to feed water to crops growing on different levels. The invention of machinery during the Industrial Revolution and the availability of fossil fuels enabled water to be moved more effectively. Machinery can now pump water from deep underground aquifers, transport it over long distances and over high elevations.
Table 1: Water Availability per Capita per Continent
The table shows that there has been a decrease in water availability over the last 50 years for all continents. It also shows that continents with the highest population densities have the lowest water availability per capita.