Countries that recycle wastewater into drinking water

English speakers like to call this "toilet-to-tap water". Word for word: water passing from your toilet bowl to your tap. It's a rather bland expression, which overlooks the many chemical, physical and biological processes involved in recycling wastewater into top-quality drinking water.

Julie Mendret, University of Montpellier

AdobeStock_620286723 ©VR studio -

While this idea may still make many people wince, it is becoming a serious consideration for more and more countries and municipalities around the globe, which are rightly concerned aboutdwindling freshwater resources. The Indian megalopolis of Bangalore, for example, is working on recycling wastewater in this way, as is Los Angeles.

In the United States, the Texan cities of Big Springs and Wichita Falls are already using this technique, known as direct potable reuse, as has the South African town of Beaufort since 2011.

Namibia has been treating wastewater for drinking since 1968

But in this field, and this remains a little-known fact, it's yet another country that remains the undisputed pioneer: Namibia. At 139th place in the ranking of countries by level of development, it may come as a surprise that this southern African state is so much in the vanguard, but when you consider the near-absence of water resources in its capital, Windhoek, it's immediately less surprising that this municipality has sought to innovate.

Aerial view of Windhoek, a capital born in the middle of the desert
Aerial view of Windhoek, a capital born in the middle of the desert. H. Baumeler/Wikimedia, CC BY-SA

In the middle of an arid plain, more than 200 km from the coast, Windhoek (population 500,000) can neither harvest the scarce rainwater, which evaporates almost immediately in its desert latitudes, nor draw from the rivers or groundwater in the surrounding area, which are only recharged to a limited extent when they are not dried up.

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In 1968, the city, then under South African domination, was also seeing its population grow at an impressive rate, when it began to recycle its wastewater and transform it into drinking water. Fifty-five years later, 30% of wastewater is recycled into drinking water in less than ten hours. The rest of the domestic drinking water comes from dams and boreholes in other parts of the country.

Potabilizing wastewater in 10 steps

To enable wastewater to be recycled as drinking water, Windhoek has set up an innovative sequence of processes that currently comprises 10 stages. It includes physico-chemical processes, such as coagulation and flocculation (addition of a coagulant to create flocs, i.e. groupings of suspended matter which then fall by their own weight and are eliminated in the sludge), as well as chemical processes such as ozonation.

In contact with ozone, the water undergoes an oxidation process that breaks down numerous micropollutants (pesticides, drug residues, etc.) and inactivates bacteria, viruses and parasites.

This is followed by the final stages of biological filtration on granular activated carbon and physical filtration (activated carbon filtration and membrane ultrafiltration) to eliminate any remaining soluble pollution. Before being sent into the water network, the water undergoes quality controls and chlorination, ensuring a disinfectant effect that lasts over time, so that the quality of the water obtained does not deteriorate during distribution.

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In recent years, the Windhoek wastewater treatment plant has welcomed intrigued and interested visitors fromAustralia, Germany, the United Arab Emirates... And with good reason, the techniques developed in Namibia remain interesting in more ways than one.

A less costly solution than desalination

For countries seeking new sources of drinking water, wastewater recycling is less energy-intensive and more environmentally friendly than seawater desalination, a technique that is more widespread worldwide. Where potabilization of wastewater consumes between 1 and 1.5 kWh perm3, desalination requires between 3 and 4 kWh perm3. What's more, desalination produces bulky waste products: salt and pollutant concentrates that are often discharged directly into the seas and oceans, disrupting ecosystems.

Conference organized by the Metropolis of Barcelona on the recycling of wastewater into drinking water in Namibia, with speakers Piet Du Pisani, in charge of wastewater management in Windhoek, and ASERA, a Spanish association promoting the recycling of wastewater into drinking water in Namibia.
Conference organized by the Barcelona Metropolitan Area on the recycling of wastewater into drinking water in Namibia, with speakers Piet Du Pisani, in charge of wastewater management in Windhoek, and ASERA, a Spanish association promoting the reuse of wastewater. Screenshot/YouTube channel of Àrea Metropolitana de Barcelona

Despite all these advantages, and the convincing results of the Namibian case study, the potabilization of wastewater is still in its infancy on a global scale, as its application involves overcoming a number of barriers. Firstly, the cost of installation. To date, only developed countries have been able to finance such projects, either on their own soil (in the United States, Singapore, etc.) or abroad, with, for example, the modernization of the Namibian plant, a public-private partnership involving the French company Véolia, the Australian-Indian company Wabag and the city of Berlin.

Financial, legislative and psychological obstacles

Secondly, legislation in the various countries is still highly restrictive. In Europe, for example, such a plant would not currently be authorized, and the only project currently underway for the potabilization of treated wastewater, the Jourdain Program in Vendée, will discharge the water into a reservoir used as a reserve for drinking water production, and not directly into the water distribution circuit: this is indirect potabilization.

And even when the funds and laws are in place to enable the direct use of drinking water from treated wastewater, a final barrier remains, and not the least: making it acceptable for a population to drink old treated wastewater, and overcoming what is known as the "yuck effect". In 2000, a wastewater treatment plant in a Los Angeles neighborhood, which had cost $55 million to build, had to close down a few days after it opened, because "never make people drink toilet water" had become a campaign promise of the politician running for mayor.

In Namibia, no such problem arose when the potabilization of wastewater was introduced, as the inhabitants of Windhoek, then under Apartheid, were presented with a fait accompli three months after the first plant went into operation. However, in an article in the Sunday Tribune in November 1968, the journalist covering the announcement of this new wastewater recycling system reported that the mayor of Windhoek at the time, in a blind test, preferred the taste of treated wastewater to that of water from conventional sources.

Archive of the November 24, 1968 edition of the South African newspaper _Sunday Tribune_, headlined "Windhoek drinks sewage water".
Archive of the November 24, 1968 edition of the South African newspaper the Sunday Tribune, headlined "Windhoek drinks sewage water".

The Singapore example

However, not informing the population upstream remains a radical solution that is not recommended, since raising awareness of the scarcity of water resources and the need for more sustainable alternatives is the best way to launch such a project. This is what led to the success of Singapore's project, which relied heavily on communication around the potabilization of treated wastewater, organizing tours of the treatment plant, for example, or showing the Prime Minister of the time calmly sipping a glass of this new recycled wastewater.

So the yuck effect turned into national pride. Pride in mastering cutting-edge technology and pride in gaining greater independence from neighboring Malaysia, which remained its main supplier of drinking water and with which diplomatic relations could be strained.

Beware of the "rebound effect

But Singapore has not put all its eggs in one basket in its quest for self-sufficiency in water resources, and has also gambled on seawater desalination, rainwater harvesting and the reduction of water consumption by its inhabitants (from 165 L per capita per day in 2000 to 141 L in 2018).

For all those who advocate better use of water resources, this sobriety is vital, both upstream and in parallel with the development of wastewater potabilization projects, in order to combat what is now known as the "rebound effect". This expression describes the uninhibited and growing use of water resources following the introduction of desalination techniques or the reuse of treated wastewater. These new water resources should only be considered as a means of meeting existing and essential needs and uses, often as a substitute for drinking water, and not as a call to create new ones.

In order to maximize the resources at our disposal, the wastewater recycling plants of the future will also have to valorize the waste produced by wastewater treatment processes, for example by transforming phosphorus and nitrogen into nutrients useful for agriculture, or by producing energy through methanization using the waste collected during treatment as input.

This article is part of a project involving The Conversation France and AFP audio. It received financial support from the European Journalism Centre, as part of the "Solutions Journalism Accelerator" program supported by the Bill & Melinda Gates Foundation. AFP and The Conversation France retained their editorial independence at every stage of the project.

Julie Mendret, Senior Lecturer, HDR, University of Montpellier

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