While space scientists ‘follow the water’ when hunting for life on other planets; the same is true on our own: all life on land depends on surface freshwater. It is found mainly in the form of rivers, lakes and wetlands. And as zones of high biodiversity these water bodies often keep local populations sustained with sustenance as well as drinking water – it being all the more important they are carefully studied and safeguarded.

These bodies owe their existence on land to the water cycle, with water vapour carried from the oceans by evaporation to fall on the ground as rain then trace their way back to the sea short with the help of gravity. But as a solar-energy-driven process, the water cycle has the potential to be disrupted by global warming.

From space, radar altimeters can monitor worldwide water levels; even trace the rate of a river’s downhill flow. Optical and radar instruments can identify any changes in area, while spectrometers can measure water quality, applying algorithms to the water colour to decipher the complex mixture of pollutants, suspended sediments and living and decomposing phytoplankton contributing to it.

And ESA’s SMOS mission maps relative soil moisture – an important climate variable – as a means of giving early warning of droughts or extreme weather.