Grey water footprint is the amount of:

Answer: [B] freshwater required for mixing and diluting pollutants enough to maintain water quality according to certain standards

Green water footprint is water from precipitation that is stored in the root zone of the soil and evaporated, transpired or incorporated by plants. Blue water footprint is water that has been sourced from surface or groundwater resources and is either evaporated, incorporated into a product or taken from one body of water and returned to another, or returned at a different time. Irrigated agriculture, industry and domestic water use can each have a blue water footprint. Grey water footprint is the amount of fresh water required to assimilate pollutants to meet specific water quality standards.

This question is a part of GKToday's Integrated IAS General Studies Module