What is Blue, Green and Grey Water?

What is blue, green and grey water?

Taxonomy

• Reclaimed Wastewater
• Water Reuse & Recycling
• Water Reclamation
• Virtual Water
• Water Footprint
• Wastewater Treatment
• Industrial Water Reuse
• Virtual Water
• Reclaimed Water
• Freshwater
• Water Recycling
• Reuse
• Grey Water
• Hydrology Cycle

6 Answers

1. The Water Network Research team has consolidated an answer to the above question. 
   Further input from members is welcome and appreciated.   

    

   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 the production chain.

   Virtual water is comprised of 3 different components:

   • Green water
   • Blue water
   • Grey water

   Different kinds of ‘coloured water’ (green, blue, grey and black-which is not virtual water) are classified based on where they are found in nature or the level of contamination of wastewater.

   
   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 the 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, it can be used for watering crops and other plants and is 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. 

    

   Related documents: 

   • A quantification of virtual water flows between nations in relation to international crop trade
   • Good water, water to “eat”. What is virtual water? 
   • Virtual water: an effective mechanism for integrated water resources management 
   • Review and classification of indicators of green water availability and scarcity 
   • Greywater Management in Low and Middle-Income Countries
   • Grey Water Treatment Systems: A Review

   1 Comment

   1. Unfortunately your answer for green water does not make sense- plants do not use water via transpiration. They take in water from the soil via absorption and then lose water to the atmosphere through transpiration. Just in case other educators/laymen are trying to understand these terms and find your site.

2. What is Green water and blue water

3. Thanks, super helpful! I never knew the difference between blue and green water.

4. The first times I encountered the concepts of "blue and green water" was in the publications of Prof. Falkenmark & Rockström. F. gave a lecture a few yeas ago in Lausanne. Here's the link to his ppt: www.siwi.org/documents/Projetcs_docu/Malin_Lausanne_March_09.ppt For info on Blue-Green Water flows, see slide 6.

5. Blue vs Green Water
   
   

   Rain fed agriculture covers 80% of the world's cultivated land, and is responsible for about 60% of crop production. In rain fed agriculture the soil stores the rain and releases it slowly to the plants. This rainwater used in agriculture is part of what is called 'green water’ and is a characteristic of the land on which it falls. It is usually not subject to competition from other sectors.

   Yields in rain fed agriculture are still far from their potential. In 2005, cereal yields were about 1.1.5 tonnes per hectare in Sub-Saharan Africa, compared with 5 tonnes per hectare in Europe. ‘Green water’ or rain fed agriculture has an important role to play in sustaining populations and securing future food supplies.

   By contrast, in irrigation, water is extracted from rivers, lakes and aquifers (which is referred to as ‘blue water'). This ‘blue water’ is applied on land, where most of is consumed by evapo transportation. Irrigation competes with other sectors (including the environment) for ‘blue water.’ Today irrigated agriculture covers about 20% of cultivated land and accounts for 40% of global food production. 'Grey water' is polluted or waste water, which can be recycled and purified. Grey water will play an important role in securing future global water supplies.

6. water footprint: Blue, Green and Grey water
   
   

   The blue water refers to freshwater

   The green water refers to water stored in soil

   The grey water is polluted water

   There are many definitions available on internet but this distinction is good to know for following debate :  globally there is enough freshwater on our planet for supporting even billion 10 persons (not if we all live like in the USA)  but if grey water with resistant radioactive or chemical wastes pollute blue and green water,   should governance include strategies of sewage and strategic water stocks?