FunNature & AnimalWhat information can be obtained from the color of...

What information can be obtained from the color of the water?

Today is March 22, the international water day. In its pure state, water is colorless; at least when it comes to a small volume. However, when we want to measure the water footprint, that is, the general indicator of the use of fresh water by users, consumers and companies, a scale of colors associated with fresh water is applied, depending on its characteristics, origin, quality and use.

There are five colors to designate the different types of fresh water, although two of them have no application in measuring the water footprint.

the blue water

It is the water that moves through the ground or under it , towards the sea. The water we find in rivers and streams, lakes, ponds, reservoirs and aquifers is blue water. Blue water can be reused. If you take water from a reservoir or a well, and use it in some way that returns it back to the same body of unpolluted surface water, it will go back to being blue water.

the green water

It is the water retained by the soil and collected by the roots of plants. Inside, they contain a continuous column of water that connects the roots with the leaves. Part of this water is incorporated into their metabolism and the production of new tissues, and another part is returned to the atmosphere in a process called evapotranspiration. All of it is green water.

Unlike blue water, which is easily usable for industry and domestic use, green water can only be used for agricultural production. It is estimated that up to 60% of freshwater flows are of the green type.

Mistakenly, green water is often assimilated with rainwater. It is true that most of the water that plants obtain comes from rain, however, in the water cycle, precipitation is also the cause of runoff, which is part of blue water.


the white water

It is one that cannot be used in any way. This is the water that, after the rain, does not get to join the runoff or the aquifers —it would be blue— nor is it retained by plants —it would be green—, but rather evaporates directly.

It does not usually enter the calculations of the water footprint, because after all it is not usable water; however, there are actions that can cause rainwater that was originally going to be green or blue to end up being white. For example, a paved land without drainage can receive rain that, without feeding any plant, ends up forming puddles that evaporate without joining a larger body of water.

gray water

All water that is necessary to dilute a contaminant to a safe level is considered gray. This category includes all forms of water contamination regardless of its origin, whether it is a direct discharge from a drain, or indirect contributions such as contamination through runoff, leaching through the soil, or even residues carried by the water. that runs off an impermeable surface, such as a roof.

the black water

These are water bodies that are polluted beyond their capacity. Waters that cannot be used in any way, and that cause damage both to ecosystems —because they are incompatible with animal life— and to human health.

Measuring the water footprint

The water footprint measures the amount of water used to produce each of the goods and services we use. It can be measured for a single process, such as growing corn or rice, for a product, such as a mobile phone or a tetra-brick milk container, for the fuel needed for transportation, or even for the entire joint activity of a multinational company.

The water footprint can also tell us how much water is consumed by a particular country or by human populations in a specific river basin or a given aquifer.

The unequal distribution of water resources in time and space, as well as the abuse of these resources by certain groups or companies , can be the cause of conflicts or crises between human populations.
Problems that can be aggravated in a situation of global change , which will not only modify rainfall regimes or water distribution, but is also increasing, among other reasons, due to anthropogenic overexploitation. That is why it is so important to measure the water footprint.

When it comes to evaluating the water footprint, an attempt is made to collect and analyze all water inflows and outflows, as well as the potential environmental impacts on the water resource . For this, the water footprint is usually measured in three of the categories.

A blue water footprint is considered to exist when water is obtained from any source considered blue, and it is evaporated or incorporated into a product that retains it. Likewise, if the water is returned to a different body of water, or if it is held for a certain time before being returned.

The green water footprint corresponds to all the water that, being retained by the plants, ends up being lost, either by evapotranspiration or by its introduction into the products. It is particularly relevant in agriculture, horticulture and forest plantations.

Regarding the gray footprint , the ISO standard that regulates the evaluation of the water footprint does not contemplate it, although many groups consider that it should be included. If done, it would be the volume of water necessary to dilute the contaminants produced by any activity, until they are completely harmless.



Hughes, D. 2009. State of the resource. In Water in a changing world. UNESCO. Navalpotro, JAS et al. 2012. Water footprint of Spain and its territorial diversity.
Geographic Studies , 73(272), 239-272. DOI: 10.3989/estgeogr.201209

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