It takes 21 litres of water to produce a small chocolate bar. How water-wise is your diet?

A small chocolate bar takes 21 litres of water to produce.

Brad Ridoutt, CSIRO; Gilly Hendrie, CSIRO, and Kimberley Anastasiou, CSIRO

Our diets can have a big environmental impact. The greenhouse gas emissions involved in producing and transporting various foods has been well researched, but have you ever thought about the water-scarcity impacts of producing your favourite foods? The answers may surprise you.

In research recently published in the journal Nutrients, we looked at the water scarcity footprints of the diets of 9,341 adult Australians, involving more than 5,000 foods. We measured both the amount of water used to produce a food, and whether water was scarce or abundant at the location it was drawn from.

The food system accounts for around 70% of global freshwater use. This means a concerted effort to minimise the water used to produce our food – while ensuring our diets remained healthy – would have a big impact in Australia, the driest inhabited continent on Earth.

Biscuits, beer or beef: which takes the most water to produce?

We found the average Australian’s diet had a water-scarcity footprint of 362 litres per day. It was slightly lower for women and lower for adults over 71 years of age.

A water-scarcity footprint consists of two elements: the litres of water used, multiplied by a weighting depending on whether water scarcity at the source is higher or lower than the global average.

Foods with some of the highest water-scarcity footprints were almonds (3,448 litres/kg), dried apricots (3,363 litres/kg) and breakfast cereal made from puffed rice (1,464 litres/kg).

In contrast, foods with some of the smallest water-scarcity footprint included wholemeal bread (11.3 litres/kg), oats (23.4 litres/kg), and soaked chickpeas (5.9 litres/kg).

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It may surprise you that of the 9,000 diets studied, 25% of the water scarcity footprint came from discretionary foods and beverages such as cakes, biscuits, sugar-sweetened drinks and alcohol. They included a glass of wine (41 litres), a single serve of potato crisps (23 litres), and a small bar of milk chocolate (21 litres).

These foods don’t only add to our waistlines, but also our water-scarcity footprint. Previous studies have also shown these foods contribute around 30% of dietary greenhouse gas emissions in Australia.

Sheep drink from a dried-up water storage canal between Pooncarie and Menindee in western NSW. Water shortages along the Murray Darling Basin have devastated ecosystems and communities.
Dean Lewins/AAP

The second highest food group in terms of contributing to water-scarcity was fruit, at 19%. This includes whole fruit and fresh (not sugar-sweetened) juices. It should be remembered that fruit is an essential part of a healthy diet, and generally Australians need to consume more fruit to meet recommendations.

Dairy products and alternatives (including non-dairy beverages made from soy, rice and nuts) came in third and bread and cereals ranked fourth.

The consumption of red meat – beef and lamb – contributed only 3.7% of the total dietary water-scarcity footprint. These results suggest that eating fresh meat is less important to water scarcity than most other food
groups, even cereals.

How to reduce water use in your diet

Not surprisingly, cutting out discretionary foods would be number one priority if you wanted to lower the water footprint of the food you eat, as well as the greenhouse gas emissions of production.

Over-consumption of discretionary foods is also closely linked to weight gain and obesity. Eating a variety of healthy foods, according to energy needs, is a helpful motto.

Aside from this, it is difficult to give recommendations that are relevant to consumers. We found that the variation in water-scarcity footprint of different foods within a food group was very high compared to the variation between food groups.

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For example, a medium sized apple was found to contribute a water-scarcity footprint of three litres compared with more than 100 litres for a 250 ml glass of fresh orange juice. This reflects the relative use of irrigation water and the local water scarcity where these crops are grown. It also takes more fruit to produce juice than when fruit is consumed whole.

Two slices of wholegrain bread had a much lower water-scarcity footprint than a
cup of cooked rice (0.9 litres compared with 124 litres). Of the main protein sources, lamb had the lowest water-scarcity footprint per serve (5.5 litres). Lambs are rarely raised on irrigated pastures and when crops are used for feeding, these are similarly rarely irrigated.

Consumers generally lack the information they would need to choose core foods with a lower water-scarcity footprint. Added to this, diversity is an important principle of good nutrition and dissuading consumption of particular core foods could have adverse consequences for health.

Workers process punnets of strawberries at a Queensland strawberry farm.
Dan Peled/AAP

Perhaps the best opportunities to reduce water scarcity impacts in the Australian food system lie in food production. There is often very large variation between producers in water scarcity footprint of the same farm commodity.

For example, a study of the water scarcity footprint of tomatoes grown for the Sydney market reported results ranging from 5.0 to 52.8 litres per kg. Variation in the water-scarcity footprint of milk produced in Victoria was reported to range from 0.7 to 262 litres. This mainly reflects differences in farming methods, with variation in the use of irrigation and also the local water scarcity level.

Water-scarcity footprint reductions could best be achieved through technological change, product reformulation and procurement strategies in agriculture and food industries.

Not all water is equal

This is the first study of its kind to report the water-scarcity footprint for a large number of individual self-selected diets.

This was no small task, given that 5,645 individual foods were identified. Many were processed foods which needed to be separated into their component ingredients.

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It’s hard to say how these results compare to other countries as the same analysis has not been done elsewhere. The study did show a large variation in water-scarcity footprints within Australian diets, reflecting the diversity of our eating habits.

Water scarcity is just one important environmental aspects of food production and consumption. While we don’t suggest that dietary guidelines be amended based on water scarcity footprints, we hope this research will support more sustainable production and consumption of food.

The author originally disclosed that he undertakes research for Meat and Livestock Australia. His disclosure has been updated to specify that the above research is among the projects to which the MLA has contributed funding.The Conversation

Brad Ridoutt, Principal Research Scientist, CSIRO Agriculture, CSIRO; Gilly Hendrie, Research scientist, CSIRO, and Kimberley Anastasiou, Research Dietitian, CSIRO

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Rising carbon dioxide is making the world’s plants more water-wise

Pep Canadell, CSIRO; Francis Chiew, CSIRO; Lei Cheng, CSIRO; Lu Zhang, CSIRO, and Yingping Wang, CSIRO

Land plants are absorbing 17% more carbon dioxide from the atmosphere now than 30 years ago, our research published today shows. Equally extraordinarily, our study also shows that the vegetation is hardly using any extra water to do it, suggesting that global change is causing the world’s plants to grow in a more water-efficient way.

Water is the most precious resource needed for plants to grow, and our research suggests that vegetation is becoming much better at using it in a world in which CO₂ levels continue to rise.

The ratio of carbon uptake to water loss by ecosystems is what we call “water use efficiency”, and it is one of the most important variables when studying these ecosystems.

Our confirmation of a global trend of increasing water use efficiency is a rare piece of good news when it comes to the consequences of global environmental change. It will strengthen plants’ vital role as global carbon sinks, improve food production, and might boost water availability for the well-being of society and the natural world.

Yet more efficient water use by the world’s plants will not solve our current or future water scarcity problems.

Changes in global terrestrial uptake of carbon dioxide, water use efficiency and ecosystem evapotranspiration during 1982-2011.

Boosting carbon uptake

Plants growing in today’s higher-CO₂ conditions can take up more carbon – the so-called CO₂ fertilisation effect. This is the main reason why the terrestrial biosphere has taken up 17% more carbon over the past 30 years.

The enhanced carbon uptake is consistent with the global greening trend observed by satellites, and the growing global land carbon sink which removes about one-third of all CO₂ emissions generated by human activities.

Increasing carbon uptake typically comes at a cost. To let CO₂ in, plants have to open up pores called stomata in their leaves, which in turn allows water to sneak out. Plants thus need to strike a balance between taking up carbon to build new leaves, stems and roots, while minimising water loss in the process. This has led to sophisticated adaptations that has allowed many plant species to conquer a range of arid environments.

One such adaptation is to close the stomata slightly to allow CO₂ to enter with less water getting out. Under increasing atmospheric CO₂, the overall result is that CO₂ uptake increases while water consumption does not. This is exactly what we have found on a global scale in our new study. In fact, we found that rising CO₂ levels are causing the world’s plants to become more water-wise, almost everywhere, whether in dry places or wet ones.

Growth hotspots

We used a combination of plot-scale water flux and atmospheric measurements, and satellite observations of leaf properties, to develop and test a new water use efficiency model. The model enables us to scale up from leaf water use efficiency anywhere in the world to the entire globe.

We found that across the globe, boreal and tropical forests are particularly good at increasing ecosystem water use efficiency and uptake of CO₂. That is due in large part to the CO₂ fertilisation effect and the increase in the total amount of leaf surface area.

Importantly, both types of forests are critical in limiting the rise in atmospheric CO₂ levels. Intact tropical forest removes more atmospheric CO₂ than any other type of forest, and the boreal forests of the planet’s far north hold vast amounts of carbon particularly in their organic soils.

Meanwhile, for the semi-arid ecosystems of the world, increased water savings are a big deal. We found that Australian ecosystems, for example, are increasing their carbon uptake, especially in the northern savannas. This trend may not have been possible without an increase in ecosystem water use efficiency.

Previous studies have also shown how increased water efficiency is greening semi-arid regions and may have contributed to an increase in carbon capture in semi-arid ecosystems in Australia, Africa and South America.

Trends in water use efficiency over 1982-2011.
CREDIT, Author provided

It’s not all good news

These trends will have largely positive outcomes for the plants and the animals (and humans) consuming them. Wood production, bioenergy and crop growth are (and will be) less water-intensive under climate change than they would be without increased vegetation water use efficiency.

But despite these trends, water scarcity will nevertheless continue to constrain carbon sinks, food production and socioeconomic development.

Some studies have suggested that the water savings could also lead to increased runoff and therefore excess water availability. For dry Australia, however, more than half (64%) of the rainfall returning to the atmosphere does not go through vegetation, but through direct soil evaporation. This reduces the potential benefit from increased vegetation water use efficiency and the possibility for more water flowing to rivers and reservoirs. In fact, a recent study shows that while semi-arid regions in Australia are greening, they are also consuming more water, causing river flows to fall by 24-28%.

The ConversationOur research confirms that plants all over the world are likely to benefit from these increased water savings. However, the question of whether this will translate to more water availability for conservation or for human consumption is much less clear, and will probably vary widely from region to region.

Pep Canadell, CSIRO Scientist, and Executive Director of the Global Carbon Project, CSIRO; Francis Chiew, Senior Principal Research Scientist, CSIRO; Lei Cheng, Postdoctoral research fellow, CSIRO; Lu Zhang, Senior Principal Research Scientist, CSIRO, and Yingping Wang, Chief research scientist, CSIRO

This article was originally published on The Conversation. Read the original article.