Virtual Water: Blue, Green and Grey Water

Different kinds of ‘coloured water’ (virtual water: green, blue, grey water ) are classified based on where they are found in nature or the level of contamination of wastewater.

The term virtual water was first defined in 1998.

It is the volume of water required for making a product and the water used in all the steps of the production chain. 

The water that is visible in our domestic use is only the small part of the water that we actually consume. 

Many people do not take into consideration or are even not aware of the huge amounts of water used in different industries (meat, dairy, textile and other industries) and the water hidden in our food. 

Did you ever think about how much water is needed for e.g. 1 kg of beef? 15400 l. 

The cow needs to be fed for three years, before being ready to eat. The food it consumes needs to be watered while grown. The farmhouse and slaughterhouse need water for cleaning and operational purposes. All in all, the come to the shocking number of 15400 litres of water to produce 1 kg of beef. 

This hidden water flow is present in all the industries in different production stages and is called virtual water. 

Virtual water is comprised of 3 different components:

• Green water
• Blue water
• Grey water

Green water is the soil moisture from precipitation , used by plants via transpiration.

It is part of the evapotranspiration flux in the hydrologic cycle.  

Blue water is freshwater : surface and groundwater.

It is stored in lakes, streams groundwater, glaciers and snow.

Grey water is polluted water which was not in contact with faecal matter.

Grey water is the product water of domestic activities: bathing, laundry and dishwashing or polluted water due to pesticides in agriculture and nutrients from fertilizers.

It can be recycled and reused, not for drinking, but for irrigation. Since it was not in contact with human waste, the it breaks down fast enough so it can be used for irrigation and safely reabsorbed into the ground.

Grey water contains soap and fat particles, even hair. If the chemicals content is not too high, majority of plants are able to handle it. However, if grey water is to be used for irrigation it is highly advised that what goes down the drain is heavily regulated.

This water flows through the man-made infrastructure. 

Black water is not virtual water and it is sewage water flushed in the toilets.

It was in contact with faecal matter containing harmful bacteria and disease- causing  pathogens.

Black water cannot be reused without risking contamination since the waste doesn’t decompose fats enough.  

Media

Taxonomy

• Wastewater Use
• Reclaimed Wastewater
• Industrial Wastewater Treatment
• Water Reuse & Recycling
• Water Reclamation
• Virtual Water
• Wastewater Treatment
• Wastewater Collection
• Industrial Water Reuse
• Virtual Water
• Water Cycle
• Reclaimed Water
• Freshwater
• Water Recycling
• Reuse
• Grey Water
• Surface-Groundwater Interaction
• Hydrology Cycle