Waste Management Market Size Worth USD 2.33 Trillion by 2034 | CAGR: 5.6%

Dr Gareth Davies ^a

^a Tunley Environmental, Sheffield, UK, garethdavies@tunley-environmental.com

5^th November 2025

1. Introduction

Here at Tunley, I am lucky enough to work in a team of PhD scientists. A big aspect of being a scientist is understanding and translating the countless complexities of life, matter, and the universe into tangible concepts. Scientists have to take complex stuff and make sense of it all. Whereas the world of bureaucracies, administration, and business take simple concepts and construct overly elaborate complex systems around them. Often these are so complicated, convoluted, and filled with miscommunication they create a barrier to tackling the main tasks at hand. Here we can step in, we aren’t the Scientists you find in a 60’s Sci-fi film causing catastrophic disaster, we are here to help! The same problem-solving approach used to explain the mysteries of the universe can explain the mysteries of bureaucracy. So, I am here to tell you to break bad! Become the Walter White of sustainability at your organisation! And take the scientific approach to make real change in the world!

Okay, maybe I got a little bit ahead of myself there. I apologise for that, but it is true, if we want to make a meaningful impact in terms of sustainability, we must cut through the bureaucracy and get to the meat of the issue. That is what we want to do today and why I included so many pop culture references in the title and the introduction. We are going to explain simply; the common terminology used in water footprinting assessments. When it comes down to it, we need water to live. It is a simple as that. Water footprinting assessments enable us to make sure that there is enough water for us in the future. By understanding these common terminologies, you shall be able to take actionable steps towards preserving that future. I think that’s enough pre-amble, let’s get stuck in!

2. Colours of Water

Often different areas default to a colour coding system to explain different aspects of materials or processes (i.e. the rainbow of hydrogen). Water is no different, a colour coding system is quite ubiquitous for water footprinting. These colours dictate the source of the water impact. The most universally accepted colours for water footprinting are green, blue, and grey. Green water is from precipitation effects (rain). When it rains, if a process uses that water, it is classified as green water usage. Green water is heavily used in agriculture. With large surface area and consistent water requirements they are poised to take advantage of natural rainfall. Blue water is the consumption of surface and groundwater resources. This is freshwater, which is available in lakes, aquifers, rivers, etc. It is estimated that only 2.5% of all water on Earth is freshwater with less than 0.5% being accessible [1]. Finally, grey water is the pollution of freshwater, quantified as the volume of freshwater required to assimilate pollutants. Conversely, grey water is also commonly used to describe and identify polluted low-quality water such a water from an industrial process.

Now there are also other colours linked to water which you may hear of or see. Only a couple of additional colours relate to water footprinting, and some other industries have colour systems related to water (adding more confusion to things). Black water is sometimes used to describe extreme water degradation in a water system. The colour is evocative of that level of degradation, and usually the discussion around black water has a lot of nuance. White water is an emerging term; it specifically represents the fraction of irrigation water that is withdrawn from blue water sources but does not directly contribute to crop evapotranspiration [2]. Secondarily to this, there are other industries that use purple, yellow, brown, red, and orange water as terms. For clarity, all of these colours are presented in Table 1 as well as the impact having a high-water footprint in that area would mean for your business, product, or service.

3. Quality of Water

You have already heard us mentioning freshwater. Almost definitely this intrinsically means something to you. Whether you are imagining a crystal-clear spring in a forest or a tall cold glass of water from the tap. Freshwater is absolutely critical to water footprinting. That is because freshwater is critical to our survival. The basis of a water footprint assessment is in measuring the freshwater consumption. However, freshwater can be defined in a myriad of different ways. Water footprinting generally uses total dissolved solids as it’s metric for defining water quality. That is how much stuff is dissolved in the water. Each of these is given in ppm otherwise known as milligrams per litre. If I dissolved a gram of salt in a litre of water, it would have 1,000 mg/L of total dissolved solids (at least plus already present dissolved solids). Would you want to drink that salty water or would you pass? Either way we shall stick with the ISO 14046 standard definitions on water quality herein. They provide three definitions for water quality based on total dissolved solids, freshwater, brackish water, and sea water (Table 2).

It is important that you are prepared and not shocked when people reference other names for water quality. However, there are too many different definitions on water quality to name here. Other water quality systems may use total dissolved organic compounds, or total dissolved heavy metals, or pathogenic content of water. What you should ask when you encounter these is “how are they defining their water quality”. Quickly followed by “What would I be comfortable doing with what they define as freshwater”. This is with the caveat that rainwater (green water) is not considered potable before treatment. You are not meant to drink rainwater due to the presence of pathogens and other pollutants. However, green water is almost always defined as freshwater.

So why does this matter? Well, what are we trying to get out of a water footprint assessment? We are trying to preserve our freshwater resources as they are highly valuable. What this means is that the consumption of any water across green, blue, grey should have the additional caveat of water quality attached to it. We should be looking to consume as little freshwater as possible and can seek to implement methodologies or techniques to use brackish water or sea water instead.

I shall leave you on water quality with this one consideration. A 200 mg dose of potassium cyanide is a lethal dose of cyanide. This means we could dissolve 0.5 g of potassium cyanide in a litre of deionised water to get a 500 mg/L concentration solution, and it would be considered “freshwater”. Not something I would want to have in my glass. It is very important to truly consider what is in the water you are classifying, what processes, what sources. Taking a more pragmatic approach is needed to go beyond the minimum standards.

4. Consumption/Use of Water

Now, when it comes to the water footprint of a product or service there are various terms related to this which may sound interchangeable, but they mean vastly different things. These terms include water consumption, water use, water footprint, and water withdrawal, and can then be further split by direct water or indirect (sometimes called virtual) water. A water footprint covers all aspects of water quantified. This is split into direct and indirect water use. Direct water use is the use of water in the actual business, product, or service. Indirect water use is from the supply chain. This is split across green, blue, and grey as previously discussed. Water consumption is defined as only the green and blue water use. Water pollution is defined as only the grey water footprint. Water withdrawals are defined as the direct blue water consumption, that is the amount of surface water being used directly by the business, product, or service. A diagram explaining all of this is shown in Figure 1. Now you are armed with this knowledge you can hopefully decipher what a particular water assessment is saying with regards to the specific water terminology.

5. Water (Hydrological) Cycle

The hydrological cycle is a fancy word for water cycle. That is the evaporation of water up into the sky and then the precipitation of that water back down again. Within water footprinting the transfer of water from the ground through plants is also considered, this is called transpiration. A combined term is therefore given as evapotranspiration. The water cycle is an essential part of our planet’s function. In our upcoming book we discuss in depth the impact that climate change is having on the water cycle and why it is happening. To put it simply the water cycle is becoming more extreme [3]. We are having longer periods of droughts and heavier rainfall. The net volume of water going up (evapotranspiration) and coming down (precipitation) remains the same.

This leads us to another important aspect of water footprinting. Areas have specific environmental flow requirements. This is the volume of water required to maintain healthy ecosystems (rivers, wetlands, etc.). We also must consider the flow requirements for human use of water in an area. Each area in question has different environmental flow requirements, precipitation effects, and availability of freshwater (i.e. reservoirs, aquifers). These are all important consideration in a water footprint assessment. If you are using a lot of freshwater for a process in an area with high availability and low environmental flow requirements there is little concern. However, if the same process were occurring and the environmental flow requirements were higher than it may require changes in the processing to prevent water scarcity.

There is a simple calculation which can be conducted. The total water footprint across the whole system is divided by the blue water availability which is given as the total natural water runoff minus the environmental flow requirements. The answer is given as a percentage, if it is above 50% is it an area to monitor carefully, if it is above 100% action must be taken to prevent water scarcity in the region. In non-maths terms you look at how much water is available in the area. You take away the natural requirements for water, leaving you with the remaining water. Your water consumption is a percentage of this remaining water. If you are using more water than is remaining, then you are using too much water and need to look at refining your process.

6. Conclusion

Now I am hopeful you now better understand that water is essential to life and understanding its use is vital for sustainability. Through learning about water colours, quality, and consumption, we can see where and how water is used in any process or business. Furthermore, recognising the balance within the water cycle helps us protect both natural ecosystems and human needs. Taking a scientific approach in this manner allows us to manage water responsibly and ensure its availability for the future. If you ever have any concerns or questions about the water your business, product, or service is using please get in touch with us. We would love to help mitigate against the emerging water related risks due to climate change.

7. References

The main references used in this white paper were the Water Footprint Assessment Manual and the BSI standard IS 14046:2016 [4], [5]. These are used throughout as the main basis and consequently not cited for any specific section.

[1]         S. Bernstein, “Freshwater and Human Population: A Global Perspective.”

[2]         A. Ashrafi, H. Ebrahimian, T. Maarefi, H. Dehghanisanij, and M. Sharifi, “White water footprint: valuable subdivision in water footprint,” Water Int, vol. 49, no. 7, pp. 849–851, Oct. 2024, doi: 10.1080/02508060.2024.2424121.

[3]         H. Douville et al., “Water remains a blind spot in climate change policies,” Dec. 15, 2022, Public Library of Science. doi: 10.1371/journal.pwat.0000058.

[4]         A. Hoekstra, A. Chapagain, M. Aldaya, and M. Mekonnen, “The Water Footprint Assessment Manual,” 2011. [Online]. Available: www.earthscan.co.uk

[5]         BSI, BE EN ISO 14046:2016 – Environmental management-Water footprint-Principles, requirements and guidelines BSI Standards Publication. 2016.