☔️ Water series: How mankind uses water? From food to energy

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From food: traces of pre-Hispanic irrigation in Peru (CC licence).
To energy: watermills were used for hard works such as hammering paper paste (paper mill) or grinding cereals seeds (gristmill) (CC licence).

The source of all our food which is also involved in most of the cooking techniques we use every day is, in fact, this basic molecule essential to life: water (H2O). It is also one of the major environmental concerns, when disputed as a ressource for humans or as a milieu for wild species. How water is the honorable “background” of every form of life on Earth, and how our relationship with it might change while facing global warming, are some of the questions that led us to this “☔️ Water series”, divided in 4 chapters:

  1. ☔️ Water series: The primordial soup of life: oceans water
  2. ☔️ Water series: Interactions of flora with water and climate
  3. ☔️ Water series: How mankind uses water? From food to energy
  4. ☔️ Water series: Future extreme dynamics of water use

Colors of water use

Agriculture uses mostly “blue water”: here to grow watercress (CC licence).
Industrial “black water” treatment plant in Poland (Wikimedia).
Steps of industrial “black water” treatment (Wikihow).

Before to dive in the complex relationship between our civilisation and water resources, a few notions may be useful to know. We will explain what virtual water; blue, green, grey and black water are; and what distinguish water withdrawal from water consumption.[1]

Blue and Green water

First of all, mankind uses “blue water”, freshwater taken from the surface or from groundwater (39% of rainwater). Among the scenarios of its human use, it might be “consumed” by several activities: it could either end up as irrigation water that evaporates in the atmosphere while sitting in an artificial lake; or it could also be incorporated into a product that might be a plastic bag as well as a vegetable or any food. An other scenario is for this water to be drawn, or “borrowed”, without being “consumed”. It could be used to transmit its gravity potential in hydroelectric water dams, by falling from a high reservoir through a water turbine in a river downstream. Or it could run through the cooling towers of a nuclear power plant before to be discharge downstream at a higher temperature. This is “water withdrawal”, where water can be released back in the ecosystem, as opposite to “water consumption”, where it enters another cycle.[2] Both terms account for “water use”. Most of “water consumption” will actually be imputable to the agriculture sector. Still, when farming, “green water” prevails over “blue water”. Despite the fact that irrigation and animal husbandry make most of “blue water” use, farming would not exist without “green water”, which is available rainwater for vegetation inside itself and in the soil of agricultural lands. As said in chapter 1, “green water” will evaporate throughout plants leaves (5% of rainwater) or stay incorporated in it. This water stock is primal for the agriculture sector, as it is the only water input for 80% of the world’s agricultural land — even though the 20% irrigated lands left produce 40% of plant’s grown worldwide.[3]

Virtual water

Those terms are of great use for environmentalists and hydrologists, because they allow a detailed description of how we use water, from citizens and cities to products and industries. To do so, they consider the direct water footprint as well as the “virtual water” footprint. Ultimately, most of Western citizens would use way less water when showering or drinking than when shopping a new shirt or eating a hamburger every now and then, as those commodities call on the use of water to be produced (respectively 2495 and 2808 litre[4]). The idea of “virtual water” was introduced in 1993 by British geographer John Anthony Allan, and granted him the Stockholm Water Price 15 years later. Following the spread of this concept, also known as “embodied water”, Swedish hydrologist Malin Falkenmark introduced the concepts of green and blue water described previously.[1] Since a few year now, NGOs like the Water Footprint Network, initiated by Dutch professor Arjen Hoekstra, are able to evaluate global average footprints of basic goods such as potatoes: 287 litre per kilogram with 66% green water (rainwater), 11% blue water (irrigation) and 22% grey water (washing potatoes).[5]

Grey and Black water

Indeed, older terms like “grey water” are used to describe the domestic water that generally goes back downstream after cleaning dishes for instance. Obviously, this water use lies in the withdrawn category, as its quantity did not change, but its quality did when it was slightly polluted (by detergent or other, excluding faecal matter). Thus, this “grey water” could require to be treated before to run downstream; but it should better be reused for other purposes such as toilets water to become sewage, thus limiting the overuse of tap-water. The “black water” obtained after “proper” pollution will then reach the sewer system. But only a fraction (20% worldwide) of it will go through the long decontamination in wastewater treatment plants, which makes it reusable downstream.[6][1]

Agriculture water footprint and climate

Level basin irrigation: rice fields in Kunming, China.
Furrow irrigation: preparing soil before sowing, in Armenia (CC licence).
The energy needed to pump groundwater for irrigation is an important source of greenhouse gas emissions from the agricultural sector (USA rice field, CC licence).
World agricultural water withdrawals in 2010 (Our World in Data).

Share of freshwater dedicated to agriculture

Agriculture is the most exploiting activity when it comes to water, with an average water footprint reaching 69% of global “blue water” use, followed by the industry[7] consuming 19% of it, and domestic uses (from tap water to pools) with 12%.[8] Nevertheless, those numbers are not representative of the variations from one country to another; considering a US citizen uses around 1543m3 of “blue water” every year, a French citizen 475m3, and an RDC citizen 11m3.[8] Not only water consumption per capita varies, but also the share of water allocated to the industry: as expected, highly industrial European countries are allocating more than 2/3 of their water resources to industries, when most countries on the African continent are using more than 3/4 of their water for agriculture, for the supply of irrigated lands.[8]

Irrigation and greenhouse gas emissions

Among all the types of irrigation systems that are used worldwide, surface irrigation is dominant with 86% of the total irrigated lands. It consists on the simplest way to spread water on land, as it is basically using gravity to bring water to the soil. It will either works by:

  • flooding an entire piece of land surrounded by soil banks (level basin irrigation);
  • or running water through small parallel channels along the fields length in the direction of the slope (furrow irrigation).

Both of this techniques are considered as less efficient than localised drop-by-drop irrigation for instance, because a share of the water input can be lost in evaporation and its distribution on crops is rather uncontrolled. Nevertheless, the benefits of surface irrigation since the early stages of agriculture is indisputable; and its adverse impacts can be addressed by an holistic management of water.[1] Unfortunately, when it comes to its carbon footprint, irrigation is among the plant farming techniques that call on the use of the bigger amount of fossil fuel because 38% of the “blue water” input comes from groundwater.[3] As groundwater tables are lower than rivers and lakes, farmers can’t rely on gravity: they need pumps, often powered with gas, to access water. Since 2010, China is the largest irrigation area, with 69M hectares equivalent to 21% of the world irrigated lands. There, 61% of the greenhouse gas (GHG) emissions of the irrigated sector accounts for water pumping and conveyance.[9] This explains why the average carbon footprint of flooded rice is 2 times bigger that of wheat.[5] As Chinese energy is far from being decarbonated, the improvement of water use efficiency seems the only effective way to reduce emissions, while reducing pressure on overexploited groundwater tables.

Water use and global responsibilities

We already know that the agriculture sector uses more water on average, and considering that the 2 leading countries in term of water use for agriculture (China and India) also have the highest share of irrigated lands; we can guess that irrigation is the main cause of water use in this sector. However, there are no legit reason to “blame” nations for the impressive amount of water they consume unless it is made without regards to groundwater recharge. Why? Because water is not like GHG emitted by fossil fuels: if someone stops using water where it is abundant, this will generally have no impact on distant places where water stress is high. Thus, to compare the industry and agriculture on the scope of GHG emissions resulting from water use; we will outline the hydroelectric dams which potential carbon footprint is often neglected. Electric plants cooling is put aside here because, while using massive amounts of water, only a fraction of it is consumed (typically 10% evaporated for nuclear plants[10]) and the GHG emissions that result are not correlated with water use.

Energy production and water use

The Grande Dixence gravity dam is producing hydroelectricity in Switzerland since 1961 (2004, Wikimedia).
World hydroelectricity per-capita production (Our World in Data).

So, let’s focus on the 2nd most used renewable energy worldwide, after biomass burning: hydropower (3.9% of worldwide energy source[8]). Hydroelectricity combines 4 different techniques:[1]

  • The water dams, basically what most of us think about when talking about hydroelectricity: it consists on an artificial reservoir of water kept by a dam, were the water flow activates a turbine generating electricity, before to run downstream.
  • The pumped-storage hydroelectricity is a sort of giant battery using water as stored potential energy. It works by pumping water downstream to store it in a reservoir upstream. When an excessive amount of electricity is produced by nuclear power plants at night for instance, water is pumped with this useless electricity. This energy would be eventually restored when needed by the dam’s turbine.
  • Run-of-the-river hydroelectricity have small or no reservoir capacity: only the energy from the water flow of the river is used. They have a lower environmental impact that of dams, because no lands need to be flooded, but power can’t be stored and controlled.
  • Tidal power uses the daily rain and fall of ocean water with the same advantages and disadvantages than run-of-the-river.

Hydropower low overall footprint

The main source of GHG emissions when it comes to hydroelectricity are reservoirs of water dams, and this apply to any dam — even when used to store water for farmers or to regulate floods (3/4 of water dams). When a vast area is flooded to make a dam, the first economical, social and environmental impacts are obvious: villages might disappear, populations are displaced, whole ecosystems are disrupted, and the carbon footprint of concrete used for the dam is not insignificant. However, hence all this happen, a new constant higher source of GHG emerges from the bottom of reservoirs: when forests are flooded, plants and other organic materials are decaying in an anaerobic environment, thus emitting methane, an impactful GHG gas (84 times more potent than carbon dioxide). Each reservoir must be evaluated separately, as their emissions vary greatly, from close to 0 (±10% of dams) to as much as coal power plants with 1000CO2eq/MWh (±10% of dams). Fortunately, a clear pattern has been found: most of the high emitting dams are situated in tropical climates, where vegetation is the densest, which results on more organic mater decaying, ergo more emissions.[11]

Hydropower beneficial potential

Still, the average electric dam accounts for less emissions per electricity produced than most solar electricity. In addition, it is important to identify the difference of origin between biomass related emissions (from reservoirs to ruminant digestion and wood burning) and fossil fuel related emissions (from oil to coal and fossil gas). The first is not adding carbon in the natural carbon cycle: it can be sustainable as long as carbon is stored again in growing biomass. The second emission brings back carbon that was eventually put out of the cycle when fossilised in the ground. By doing so, mankind disrupted the overall cycle as it used to work before the industrial revolution.[11] Off course, considering only the carbon footprint scope is not enough, and agriculture or reservoirs have their shared effort to make to mitigate climate change. But since more than 80%[12] of the energy consumed still rely on fossil fuel worldwide, and several countries are not using the full potential of their hydropower; we advocate for an energy mix that will foster hydropower at the expense of fossil fuels. Among the regions with the highest potential, Africa, the Middle East and Asia-Pacific are limited by the lack of fundings and/or political stability, as bordering countries downstream the rivers where dams are built can be impacted by water flow variations.[4] On the other side, Western countries like the Canada, the US and Russia seem shy to develop their hydropower potential, probably for political reasons related to their important fossil fuel resources. To conclude, it is important to state that most Northern countries — even the ones already exploiting more than half of their potential hydropower (Switzerland, Norway, Sweden, France, Austria, Japan) — should bet on the reduction of their overall energy consumption rather than new sources of renewable energy, since their carbon footprint per capita is already the highest since the beginning of the industrial era.[11]

Notes

  1. 1.0 1.1 1.2 1.3 1.4 source: Wikipedia pages:
  2. The definition of both terms might slightly vary in the US, where brackish water and sea water withdrawals are considered too. Some consider “water consumption” as a part of “water withdrawal” but we find it more convenient do separate the 2 by considering the last as the water that is not consumed; and the addition of both as “water use”. source: Tom Gleeson, “What is the difference between ‘water withdrawal’ and ‘water consumption’, and why do we need to know?”, Water Underground blog, AGU blogosphere, 2017. https://blogs.agu.org/waterunderground/2017/06/26/difference-water-withdrawal-water-consumption-need-know/
  3. 3.0 3.1 source: Data visualisation document by AQUASTAT, FAO’s global water information system, 2014. http://www.fao.org/3/I9253EN/i9253en.pdf
  4. 4.0 4.1 source: (FR) «Atlas de l’eau», Courrier International hors-série, septembre-octobre 2020. For water conflicts, see: Turkey and Irak, Ethiopia and Egypt/Sudan, Israel and Jordania. In the chapter «Rivalités», p.46.
  5. 5.0 5.1 source: Water Footprint Network website, “Product gallery” https://waterfootprint.org/en/resources/interactive-tools/product-gallery/
  6. “Globally, 80% of black waters flows back into the ecosystem without being treated or reused, contributing to a situation where around 1.8 billion people use a source of drinking water contaminated with faeces, putting them at risk of contracting cholera, dysentery, typhoid and polio.” source: https://www.unwater.org/water-facts/quality-and-wastewater-2/
  7. The industry does not include hydroelectricity production by dams, as it is considered as minimal consumed water (we will consider it for its GHG emissions). On the other hand, electric plants cooling (either from gas, coal or nuclear energy) makes around half of the industrial consumption, even though only a fraction of the water withdrawal evaporates from cooling towers as steam.
  8. 8.0 8.1 8.2 8.3 Our World in Data, “Water Use Stress” webpage:
  9. In China, 50 to 70% of the GHG emissions emitted by energy in this sector are attributed to irrigated agriculture, even though it represent 11% of the Chinese agriculture surface (Our world in data). source: https://link.springer.com/article/10.1007/s11027-013-9492-9
  10. Still, this fraction of water consumed by the electricity production sector accounts for more than half of the water used by the industrial sector in Europe in 2014 — which might be easily extended to the whole world, even though we could not find datas about this. Moreover, water withdrawal is a limiting factor in this sector, as power plants must sometimes be “paused” when the water available upstream is too warm, and its temperature raise after the journey through the cooling system might impact the ecosystem downstream. source: https://ec.europa.eu/eurostat/statistics-explained/pdfscache/33684.pdf
  11. 11.0 11.1 11.2 (FR) “Le Réveilleur” youtube channel: “L’hydroélectricité” (2018) source: https://www.youtube.com/watch?v=71EopUDDJ04
  12. Our World in Data, “Energy” webpage:
    • See “Energy consumption by source, world”.
    • See “Per capita energy consumption”.
    source: https://ourworldindata.org/energy