The water footprint indicates the extent of water use relative to human consumption. The water footprint of an individual, community, or business is defined as the total volume of freshwater consumed by the individual or community, or used for the production of goods and services produced by the business.

The water footprint can be measured physically simply as a volume (in units of liters or cubic meters). Other measures, often referred to as water density (water consumption density or water footprint density), are obtained as a ratio of volume to a unit of production; for example: volume per unit of energy in the energy production sector (cubic meters per watt-hour), volume per unit area in the agricultural sector (cubic meters per square kilometer), volume per unit of mass in the manufacturing sector (cubic meters per ton), etc.

Blue water footprint
The blue water footprint refers to the volume of water taken from surface or groundwater sources (lakes, rivers, wetlands, and aquifers) that is either evaporated (e.g., when irrigating crops), incorporated into a crop, or taken from one body of water and returned to another, or returned at a different time. Irrigated agriculture, industrial and domestic water use all have a blue water footprint.
Green water footprint
The green water footprint refers to the amount of water from precipitation that is lost through evaporation or absorbed by plants after being stored in the soil's root zone (green water). It is particularly important for agricultural, horticultural and forestry products.
Gray water footprint
The gray water footprint refers to the volume of water required to dilute pollutants (industrial discharges, seepage from waste ponds in mining operations, untreated municipal wastewater or pollution from common sources such as agricultural runoff or urban runoff) to a degree that the water quality meets accepted water quality standards.