The green water footprint is an indicator of the human use of so-called green
water. Green water refers to the precipitation on land that does not run off or recharge the groundwater but is stored in the soil or temporarily stays on top
of the soil or vegetation. Eventually, this part of precipitation evaporates or
transpires through plants. Green water can be made productive for crop growth
(but not all green water can be taken up by crops, because there will always be
evaporation from the soil and because not all periods of the year or areas are
suitable for crop growth).