The human water cycle

Our increasing need for water is forcing us to examine how humans are impacting our water supply - how we obtain, use and dispose of water.

Water, an essential building block of life, constantly moves in a hydrologic, natural cycle that flows in a continuous loop above, across and even below the Earth’s surface. But water is also constantly moving through another cycle – the human water cycle – that powers our homes, hydrates our bodies, irrigates our crops and processes our waste. The tight connection between the human water cycle and natural water cycle makes them dependent on each other.

Our increasing need for water is forcing us to examine how humans are impacting our water supply – how we obtain, use and dispose of water. Initially, access to water defined where humanity could grow and develop. But now the opposite is true, and we’re the ones directing the future of our global water system. Watching this transition unfold is as sobering as it is stunning.

This three minute video, created by Felix Pharand five years ago for the opening of the Bonn meeting in Germany (meant to highlight major global water research), charts the global impact of humans on the water cycle.

Societies have come to depend on a reliable supply of water in almost everything that we do. So if that’s disrupted in any way, there are big social and economic consequences.

The problems with water are too numerous to list. They range all the way from growing populations, to accelerated usage from upgraded living conditions, to wanton pollution, to global warming and shifting weather patterns. And the consequences of our actions are unsettling – 800 million people have no safe drinking water, and four out of five people across the entire world face risk to their water security.

What is the human water cycle?

In the natural water cycle, water molecules evaporate and transpire from water on the Earth to the atmosphere, condense into clouds, come back to the Earth through precipitation, and then make their way back to water bodies though runoff and infiltration in nature.

On the other hand, the human water cycle describes how humans get, use and reuse water. The water that we drink comes from lakes, rivers, streams, glaciers, and even groundwater. It is treated and piped to our homes, flowing out from taps for our usage. Used water then goes down the drain and is transported to the sewer system, which brings it to wastewater treatment plants where organic carbon and nutrients are removed before it can be safely release back into the environment.

The way we use water is a cycle, where cleaned wastewater ends up in one of the same places that we get our drinking water.

Examining each part of the human water cycle

As expected, the cycle has multiple points of entry for contamination and loopholes where not all of these substances are removed, creating challenges and a shortage of treated, clean and safe water for our consumption.

How do we better manage the water that we’ve got? Do we build more reservoirs and wells? Do we develop more efficient technologies? These are questions that come into play when we try to think about how we are going to ensure reliable water supply well into the future.

While we are working toward solutions that will benefit us all, it helps to understand how the human water cycle works and what happens at each step.

Let’s examine each stage in detail.


Wastewater is liquid effluent derived from domestic sewage or industrial sources that cannot be discarded in its untreated form into lakes or streams due to public health, economic, and aesthetic considerations.

Here are some examples of common contaminants in wastewater:

Organic particlesFecesFood etc.
PharmaceuticalsUrineDumping of drugs in toilets/sinks
Cleaning agentsWashing (clothing, dishes)Cleaning

Domestic sewage presents a higher risk of contaminating water with the presence of problematic substances such as pharmaceuticals, coming from urine and the disposal of old drugs in toilets and sinks. It is also not as controlled or regulated as industrial wastewater.

Most of the time, normal wastewater plants cannot extract every substance and their derivative from wastewater. The extraction steps don’t work because these contaminants are too small and light to be filtered out, and have high metabolic stability to be removed via biological treatments. In addition, they even induce other problems in the plant, including disrupting the biological degradation step by killing the bacteria needed in the process.

These critical substances then which reach the next step in the human water cycle – surface water. Close to 100 different substances were found in surface waters, posing a high risk for the environment by damaging flora and fauna, and contributing to the growth of resistant bacteria or superbugs.

Surface water and groundwater

Surface water comes from precipitation that flows across surfaces (runoffs) to streams or from groundwater that appears at the surface in lakes, rivers, and more.

Meanwhile, groundwater is water that has drained through surface layers of soil and rock until it reaches a layer of rock material through which it cannot pass.

Here are some examples of common contaminants in surface and groundwater:

Contaminate Source
Pharmaceuticals Veterinary medical productsIncomplete extraction of waste and surface water
Fertilizers Agriculture
Heavy metals Dumps and contaminated sites runoffs Incomplete extraction of surface water

These substances affect the ecology and could lead to the creation of carcinogenic substances like nitrosamine. For example, nitrate from fertilizers cause the excessive growth of water plants and algae, upsetting the ecosystem and crowding out other water organisms with the lack of oxygen and food sources. Furthermore, drinking water plants have no treatment step for the removal of nitrates in surface water. This provides a potential risk for young children; a high nitrate value in drinking water (above 50 mg/l) could lead to the blue baby syndrome, as an acceptable nitrate value for babies is at 10 mg/l).

These contaminants then reach the next stage in the human water cycle, drinking water plants and possibly drinking water.

Drinking water

Drinking water is water that is safe to drink or to use for food preparation, without the risk of getting health problems. However, contaminants are regularly found in tap and drinking water. Without a doubt, the contaminants then enter the next stage in the human water cycle – you.

Water issues are ongoing and prevalent across the globe. From Delhi to New York, water containing microplastics, pharmaceuticals, heavy metals, nitrates, and all other kinds of contaminants are flowing out of taps and into our bodies. This goes to show that the contaminants that we introduce to the environment through our water ultimately comes back to us.

The realization that water treatment plants cannot handle and remove all these contaminants that are in our wastewater drives this point home. The human water cycle does not just have an impact on our environment or other species, but comes full circle and returns the contaminants that we dump out back to us.

What can we do?

There are countermeasures to prevent or alleviate the negative impacts of the human water cycle.

Take, for example, the presence of pharmaceuticals in our waste, surface, and drinking water. Some ways to stop the this from happening is to always consider environmental impacts and taking these risks into account when creating new drugs. Medication can also be offered in smaller packages, reducing the need to dump large amounts of drugs into our water cycle. The practice of getting rid of old drugs through pharmacies and hazardous waste collection points can be spread through education and awareness campaigns.

Additional treatment steps such as active carbon filters, reverse osmosis, ozone treatment, and nanofiltration, can also be added to wastewater treatment plants to ensure the thorough removal of contaminants. However, it’s important to note that these different methods are not on par when it comes to purifying water. For instance, active carbon filters are excellent at removing organic chemicals like chlorine but ineffective with inorganic substances like nitrate.

In 1991, the EU Nitrates Directive was put in place to protect water quality across Europe by presenting nitrates from agricultural sources polluting ground and surface waters and by promoting the use of good farming practices. Even though this legislation will take some time to come into effect as agricultural runoff could take years to reach groundwater, stable progress has been noted.

Similarly, the German Fertilizer Ordinance in 2017 was implemented to reduce nitrate emissions from agriculture to water bodies in the EU. In addition, we can also consider establishing of water protection areas, where agricultural activities are limited in the surrounding region.

The above-mentioned might be expensive measures, but are effective in mitigating and preventing the human water cycle from putting both the environment and our own health at risk.

At the moment, scientists and engineers around the world are studying the connections between water, food and energy in the human water cycle to develop other new, sustainable ways of meeting our water needs.

Two water cycles, one natural, one human-made, yet both are fundamental to meet our growing needs for water, food and energy. With this awareness, rallying cries and actions, we will be able to improve traditional water management and provide enough clean water for future generations.

By Mitte Team — May 30, 2018
The information contained in this article is provided for educational and informational purposes only, and should not be construed as health or nutritional advice.

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