green water
/ˌɡriːn ˈwɔːtə/noun
1Water coloured green by algae or other organic matter.
- Originally used with reference to the waters of the Nile at the onset of its annual flooding..
2 Environmental Sci. In water resource management: water that is directly derived from rainfall and used by plants or stored in the soil.
Origin
Early 17th century (in an earlier sense). From green + water.