A perspective for the acceptance of water reuse: history of the valorization of wastewater throughout the development of society

The development of society is directly related to the geographic distribution of water and its political use (Boccaletti, 2021), and to the use or final disposal of waste/wastewater (Halliday, 2019). Although the current technical-scientific area is fully aware of the benefits of wastewater (WW) for various purposes, society still strongly rejects this product. This is because modern society believes that WW causes disease, is malodorous and, when improperly disposed of, allows the development of an environment conducive to the vector proliferation.

However, current technical-scientific knowledge demonstrates the feasibility of using by-products from WW treatment, such as: (i) biogas, from the WW sludge anaerobic digestion, has a high potential for use as an energy source; according to Pasciucco et al. (2023), the use of biomethane to replace gasoline stands out as an important option against global warming; (ii) sludge produced in WW treatment has a high nutritional power for agriculture and may become an important raw material for the sustainable production of fertilizers, with a low carbon footprint (Chojnacka et al., 2023); (iii) finally, the water used to transport wastes, from the point of generation to treatment, can be reused as an alternative and sustainable source of water for several purposes (Santos et al., 2022). This is recycled water or reclaimed water (RW), the main topic of this paper.

In the past, without current scientific knowledge, wastes were used in agriculture, for soil fertilization (Angelakis et al., 2018). Currently, many water reuse plants are already in operation around the world, for agricultural, urban, industrial, and even drinking purposes (Jones et al., 2021; Santos et al., 2022). The evolution of the technical-scientific knowledge allowed and guided the construction and structuring of regulation at a global level, which began in the last century.

Although advances are substantial in relation to water reuse around the world, there are still many challenges to be overcome to ensure a safe and responsible practice. In general, the challenges involving the rejection, regulation and contextualization of the integrated management of different water sources are known (Angelakis et al., 2018; Shoushtarian & Negahban-Azar, 2020; Santos et al., 2022). However, the pressures imposed by climate change have become more evident and dynamic, requiring more forceful actions. Thus, Fernandes & Marques (2023) state that one of the main challenges is to put into practice the theoretical concept of the circular economy, particularly in the water and WW sector.

In this context, there is a tendency to shape more efficient water management, which involves the regular practice of water reuse, in addition to other actions such as reducing consumption, recycling and controlling losses (Fernandes & Marques, 2023). This more efficient water management permeates the difficulty in advancing adequate policies with the involvement of different aspects: (i) legal: adequate regulation; (ii) social: acceptance versus rejection; (iii) economic: pricing; and (iv) environmental: guaranteeing water to users (upstream and downstream) of a basin (Angelakis et al., 2018; Fielding et al., 2019; Santos et al., 2022; Fagundes & Marques, 2023).

It is important to highlight that the term ‘water reuse’ is more recent than the term ‘wastewater reuse’. Indeed, WW is always used (and not reused) indirectly, as it is discharged into water bodies, upstream of communities. Therefore, when the intention is to recover or recycle water from WW, the more comprehensive term is ‘water reuse’. In the specific case of agricultural irrigation, when nutrients are used in addition to water for fertilization, the term ‘wastewater reuse’ is more appropriate. However, currently, the term ‘water reuse,’ in a broader sense, has been more widely adopted in the context of the direct application of the practice, where water is recycled or recovered from treated wastewater (TWW). Furthermore, the term ‘wastewater reuse’ may contribute to the rejection of the practice, while ‘water reuse’ may enhance its acceptance.

The article highlights the evolution of the relationship between society and WW, from ancient to contemporary times. In this sense, the text was constructed based on a historical timeline. Posteriorly this introduction, item 2 contextualizes water reuse in different countries. Item 3 presents the concept developed in the research that involves the valorization, devaluation and revaluation of WW throughout the development of society. Item 4 presents historical facts and artistic-cultural manifestations divided into four major periods: (4.1) Ancient Times, (4.2) Medieval Times, (4.3) Modern Times, and (4.4) Contemporary Times. Finally, item 5 presents the main conclusions of the study.

In this sense, the study aims to contribute to a broader understanding of a relationship between human beings and WW as a tool for building a real and successful water reuse culture in a global level.

Faced with advances in water stress, imposed by climate change and population growth, especially in arid and semi-arid regions, the management of water resources has become increasingly complex. In this sense, water reuse can be an important management tool, in the concept of CE, aligned with sustainable development.

Currently, many countries in the world present important advances in the institutionalization of Water Reuse from TWW, with specific characteristics related to their regional scenarios and climate contexts:

• Israel: According to Marin et al. (2017), the country uses almost 90% of its TWW for agricultural purposes, thus reaching 40% of its water demand for irrigation.

• China: According to Hu et al. (2021), the country has been making major investments in water reuse, increasing from a total volume of approximately 7 billion m³/year in 2017 (Liao et al., 2021) to over 12 billion m³/year in 2019 (Hu et al., 2021).

• United States: Since the early 2000s, the country has used approximately 10% of its TWW (more than 13 billion m³/year) in several applications (Diemer, 2007), has already more than 50 potable reuse plants (direct and indirect), planned and constructed (Mukherjee & Jensen, 2020).

• Singapore: According to Lim & Seah (2013), the country has an extensive diversification of its water sources, considering local collection, imports from the Johor region (Malaysia), desalinated water and RW. Until 2018, NEWater (RW produced by PUB – Singapore's National Water Agency) had met around 30% of the country's water demand; it currently attends 40% and, in the future, it is expected to attend 50% (Santos et al., 2022). According to Lefebvre (2018) NEWater production exceeds 80 million m³/year.

• Australia: Due to its climatic conditions, the country has been investing in potable reuse, and was the first in the world to publish legal guidelines for potable reuse, in 2006 (Khan & Anderson, 2018). The two main potable reuse plants in operation in the country (Perth and Western Corridor), have together a production capacity of more than 1 billion m³/year of RW (Khan & Anderson, 2018).

• Namibia: The country features the oldest direct potable reuse plant in the world (since 1968), with a maximum capacity of 21,000 m³/day (Wallmann et al., 2021). Currently, more than 400,000 inhabitants in Windhoek are supplied from direct potable reuse (Lahnsteiner et al., 2018).

All countries mentioned are prominent regarding water reuse and consider different characteristics, which are summarized and presented in Table 1. Israel is in a semi-arid region, and water reuse is a fundamental condition for establishing its agricultural production. China, with an intense economic growth program, uses RW to minimize the risk of water shortages in its industrial sector. The United States, with non-potable reuse already institutionalized and established, currently encourages potable reuse in several states, including the publication of guidelines at the national level. Regarding potable reuse, Australia provides resources and technical-scientific knowledge for this purpose to guarantee human supply in situations of more severe droughts. Singapore has ensured its water independence from Malaysia based on a robust water reuse program, initially for human supply purposes and currently, with greater production for industrial purposes. Finally, Namibia has been practicing direct potable water reuse for more than 50 years.

In general, according to Jones et al. (2021), approximately 50% of the potable water generated is treated and 11% is reused in a planned manner. It is observed that countries in more severe situations of water stress, such as Israel, Singapore, and Australia, have high percentages of water reuse in relation to TWW. Countries like the United States and China, the two largest economies in the world, have chosen the production of water from alternative sources, with high absolute values in relation to the others. Most of the RW in the world is used in agricultural irrigation, although potable reuse has already been successfully practiced. However, only Namibia, South Africa, and the United States have direct potable reuse plants currently in operation (Santos et al., 2022).

Although water reuse has advanced in numbers, there are still some complex strategic and logistical gaps to be overcome. Fagundes & Marques (2023) highlight the task of defining specific pricing policies, as the rules applicable to drinking water and WW tariffs may not be suitable for this market. These issues consider local specificities (environmental conditions, institutional arrangements, and technical and economic aspects), which make it difficult to transfer experiences between countries and, consequently, decision-making.

However, Santos et al. (2022) point to the definition of adequate regulation to involve aspects that allow progress in a safe way and guarantee legal, economic, technical, social, environmental and health viability.

Faced with the worsening drought scenarios, the consolidation of the water reuse practice in a safe, responsible, and planned manner may be one of the joint solutions for more efficient water management globally, including as a driver of the economy (WE, 2020).

Although the benefits of water reuse are consolidated in the scientific community, its institutionalization still faces serious challenges to be overcome, even in the regions most affected by water scarcity (Angelakis et al., 2018; Santos et al., 2022). Its systematization strongly depends on the engagement of society (Salgot & Folch, 2018). Thus, the development and application of social education actions are considered essential, to minimize the effects of natural psychological rejection of water reuse, both from decision makers, technicians, users and the civil society.

Historical knowledge of the evolution of the relationship between human beings and WW is fundamental for the success of the construction of a real and successful water reuse culture on a global level. This list considers the implementation of sanitation infrastructure, the control of waterborne diseases and aspects related to the water reuse for various purposes. In this sense the present work aims to construct a general understanding of the triad valorization (V) – devaluation (D) – revaluation (R) of WW related to the historical development of society.

The concept ‘VxDxR/WW Historical Development’ was conceived on a scientific basis, involving the values (valorization, devaluation, and revaluation) internalized to WW throughout the development of society, based on facts and historical periods and artistic-cultural manifestations in each period.

The historical and scientific aspects, in addition to the cultural manifestations adopted in the construction of this concept, were based on the authors' prior knowledge and academic experience, including the development of their scientific research on this topic, over years and decades. As it is a subjective approach, possible methodological limitations can be highlighted such as the failure to address some historical passages and cultural manifestations. However, it is understood that these possible limitations do not affect the general understanding.

On the other hand, the artistic-cultural manifestations in each historical period reflect the habits, the way of life, and the social movements that help scientists and researchers to understand the facts and illustrate history. More than that, in general, culture drives the understanding of society, and science bases its decisions on it.

In such a way, in relation to the historical facts and periods, besides the artistic-cultural manifestations, we understand the urgent need to intensify the relationship of the sector with society. Understanding the historical path of the actions that led to the valorization, devaluation, and the need for revaluation of WW empowers society, in the sense of allowing it to actively participate in the construction of this knowledge and reduce the impacts of rejection, known as ‘Yuck Factor’. Salgot & Folch (2018) state that end users should be included in decision-making, for a greater chance of success with project implementation.

The aim of this paper is to build a general understanding of the triad valuation x devaluation x revaluation of WW with the historical development of society. The intention is to contribute with a tool for the purpose of building a society committed to the revaluation of WW in face of the water reuse practice.

This item presents historical facts and artistic-cultural manifestations in the context of the main historical periods reported. They help in understanding the social movements that led to the valorization and devaluation of WW, as well as the attempt at revaluation that follows in the contemporary period.

In the past, the growth of permanent settlements led to the development of WW and rainwater collection systems. The first indications of the use of WW for irrigation and fertilization of agricultural land are from around 3,000 BC, a period that matches with the beginning of the Bronze Age. This scenario can be clearly observed, especially in the Minoan and Indus Valley civilizations.

According to Halliday (2019), in the town of Harappa, all houses were connected to the main sewerage ensuring a proper removal and conduction of WW. From the dwellings, connections, and conduits were interconnected to the main system, reaching rivers, canals, and/or farmland.

In practice, cisterns (seen in Figure 5 as cylinders) were connected to canals in the streets, made of clay and covered with stone, for the conduction of solid waste, mixed with rainwater (Halliday, 2019). This demonstrates the sophistication of the systems, including the fertilizer potential of WW at the time. Removal of the solids deposited in the conduits, for manual application to crops, could be accomplished by removing the stones that covered the conduits.

Although this understanding is not clear from history, it is reasonable to assume that the practice of using WW in agriculture as a fertilizer evolved from the observation that plants grew better where wastes were deposited, either above or below the soil surface.

The Grand Tour circuit was a part of the educational process for young European nobles, as a form of supplementary education. Wealthy families would entrust their children to tutors on cultural trips lasting from months to years, with the goal of instilling in them cultural aspects of society. Visits to art museums and other cultural manifestations were then made to develop the youngsters' artistic knowledge.

In this period, as previously reported, the technical-scientific and infrastructural advances happened almost only in relation to war equipment and similar aspects. Europe was in constant conflict at this time, the main objective being to conquer territories. The water supply, which was quite advanced in the Roman period, suffered a major setback. The new civilizations of the Middle Ages began to collect water from polluted rivers in the cities or from wells dug near ditches and animal dung dumps. The advances of water intakes in rivers with good water quality, even at long distances, were over.

Sanitation services became managed by the population itself, without any quality criteria (Halliday, 2019). Both water and WW lost their value to society, and it is for this reason that this period was disregarded from the concept ‘VxDxR/WW Historical Development’. The proliferation of disease marked this period of history, which led to a new chapter in society's development regarding water and WW.

The period after the Middle Ages, known as a transition to the Modern Age, was marked by a resumption of interest in sanitary infrastructure. In this period, the occupation of nightesoilmen arose, whose task was to clean the cesspools of the wealthier dwellings. The nightsoilman usually offered the services of cleaning cesspools, as well as chimney sweeps. The material removed from the pits was disposed of in the river and often sold to farmers for use as fertilizer. Even advertisements for land sales in England showed very high values, stating that the land had been fertilized with WW for many years; in this context, it was considered productive. In Scotland, the land was offered for sale at very high price for the time, based on the assumption that it had received WW for 86 years (Halliday, 2019).

Thus, the concept of sewage farms that used WW as fertilizer was emerging. These farms began to fall into decay in the 19th century as a result of the development of WW treatment technologies for subsequent discharge into water bodies in the post-Industrial Revolution period, which began in the second half of the 18th century.

Still in the 18th century, there was an interesting moment of declared valorization of WW by philosophers and political-cultural influencers of the time. The philosopher Pierre Leraux created the so-called Circulus doctrine. This was a socioeconomic doctrine that proposed that excreta should be collected by the state as taxes. Although most people did not support the idea or even care for it, Leroux claimed that if people were more educated, then ‘everyone would religiously collect his excrement to give to the State (the tax collector) in place of the personal tax or fee. Agricultural production would immediately double, and poverty would disappear from the face of the earth’ (Halliday, 2019).

Victor Hugo, an important writer and influencer of the time, and a friend of Leraux as well, shared the idea, having written in his most important work, Les Miserables, that Paris was throwing 25 million francs a year into the water. Also, the author described the sewers as ‘gold flowing from handfuls,’ making a defense of the doctrine, although he never called it by name (Halliday, 2019; Hugo, 1862 - Excerpt ‘The Intestine of Leviathan’).

Currently, the concept of Circular Economy matches the Circulus Theory, given the proper proportions, as it associates economic development with more efficient use of resources, prioritizing their reuse. In this context, Sgroi et al. (2018) suggest a holistic approach to the sustainable implementation of water reuse, considering political, decision-making, social, economic, technological, and environmental factors, in order to enable a paradigm shift. However, in the literature review carried out by Fernandes & Marques (2023), the authors state that the main motivations for this application are still based on economic, technological, and environmental factors; legal, institutional and political factors still require greater attention. Both Sgroi et al. (2018) and Fernandes & Marques (2023) highlight the importance of this behavioral change for determining new policies, with the aim of boosting more efficient WW management, with a focus on resource recovery.

Although the historical contextualization of the eighteenth century, with the influence of the Industrial Revolution, takes into account mainly the new labor relations and socioeconomic development, as well as the widespread air pollution, it is important to highlight its specific relationship with water. On the one hand, water was the raw material for the generation of hydraulic energy in water wheels, which, although developed in the ancient civilizations of Greece, remained competitive with the steam engine at the beginning of the Industrial Revolution. On the other hand, the increased production of liquid effluents and solid waste from the industrial process strongly contributed to water and soil pollution in an environment already degraded by previous societies.

One might also mention that this period was marked by the disproportionate advance of population growth and mass migrations of rural inhabitants to the cities, in search of new opportunities. Therefore, one may believe that the population increase defined a new path for land use and occupation. The areas available for sewage farms started to disappear, encouraging the search for new WW treatment technologies that would occupy smaller areas.

In view of this scenario, it is inferred that, at that particular time, WW started to be seen as a smelly residue and disease carrier. Thus, WW was not seen any more as a potential fertilizer and source of water for irrigation. In this context, the rupture of WW valorization stands out, thus beginning a new era of WW devaluation.

The beginning of the 19th century was marked by a wide dissemination of diseases and epidemics, such as cholera, which spread through Europe, the United States, and Asia. Initially detected in India, cholera quickly reached Europe from merchants who freely transited between these areas and brought with them the cholera vibrio, responsible for transmitting the disease (Halliday, 2019).

In this period, an artistic-cultural manifestation that was gaining momentum (to the present day) was the cartoon, a humorous drawing with a tone of social criticism.

It is noteworthy that in this period, people still believed in the Miasma Theory, formulated in the 17th century by the medical scientists Thomas Sydenham and Giovanni Maria Lancisi. The theory held that diseases were caused by foul smells emanating from the putrefaction process of the organic matter present in the soil and on water surfaces. At the time, the anaerobic biological decomposition process that releases hydrogen sulfide gas, which is responsible for the odor, was not yet known.

Then, in 1849, the medical scientist John Snow, in London, stated that cholera was a waterborne disease, transmitted by contaminated water. However, as already mentioned, the Miasmatic Theory was still predominantly accepted in the scientific community and his Microbial Theory was refuted.

In 1905, Robert Koch, based on the existing knowledge regarding the waterborne transmission of the disease, won the Nobel Prize in Medicine for containing a new cholera outbreak in the city of Hamburg. He advised people to drink boiled water and to use other sources of uncontaminated water. During this period, stations to boil water were built in public areas, public bathrooms were closed, and the consumption of raw fruit was forbidden (Halliday, 2019).

In 1858, by the time that his microbial theory was effectively validated and accepted, by both the scientific community and public authorities, this pioneer of research and knowledge of cholera, Jonh Snow, had already passed away.

Throughout this period, a new understanding of diseases and WW began, not of the effluent itself, but of the WW collection, removal, and treatment, for the prevention of diseases.

It was at that time, at the end of the 19th century, that Napoleon III looked for the modernization and the urban reform of Paris, together with the city's mayor, Geroges-Eugene Haussmann (Halliday, 2019). One of their major actions, looking for the urban reform of Paris, was the construction of ‘Paris Sewers’. The goal was to transport WW away from the people, in order to protect them from contamination and ensure public health.

It is important to highlight that, in this period, the Miasmatic Theory had not yet been replaced by the understanding of the Microbial Theory in disease transmission, as previously reported. Thus, the main intention for the construction of the sewers of Paris, by conducting them to an area far away from the neighborhood, was related to the possibility of generation of bad odors. Only later would the great achievement of this action be understood.

What is interesting is that Napoleon III intended to perpetuate himself in power. In his understanding, one of the ways to achieve his goal was to set out to reconstruct the city, which naturally included water and WW services as an integral part of his plan. Even the unemployed population was used in the infrastructure works (Halliday, 2019).

The photos in Figure 14 are from 1920 and 1903 (left and right, respectively). Yet, from the 19th to the 20th century, one can notice that a cultural transformation takes place, in relation to the acceptance and even to the existing sewer system. At that time, a new point in the story of WW valorization could be seen. This point was guided by the valorization of the infrastructure and engineering works, and not exactly for the fact that collecting and treating the WW is the right way to prevent diseases and a guarantee of a healthy life. Unfortunately, contemporary society has lost any respect or admiration for the service, without realizing that a safe life in modern cities is impossible and unhealthy without WW collection, transportation, treatment, and right final disposal services.

It can be said that the discussion on water reuse in Contemporary Times starts in the state of California/USA regarding the regulation of the practice in that state. California is a region known for its local water scarcity, and for general approaches to resource conservation and sustainability.

According to Olivieri et al. (2020), in 1910, around 35 communities in California used WW for irrigation without any treatment and 24 after septic tanks. WW disposal on sewage farms was accepted as a form of both treatment and final disposal.

Over time, urban areas began to be located too close to the sewage farms and at this point, they gave way to modern WW treatment plants. Actually, there was great concern about odors and health risks associated with the application of raw sewage to the farms. Biological waste treatment technologies, developed between the 19th and 20th centuries (Salgot & Folch, 2018), required much smaller areas and allowed WW to be discharged into the sea, rivers, and streams.

Until the early 20th century, there were no significant regulations or restrictions on the use of WW for agricultural irrigation. As the scientific knowledge of the disease became more widely understood, concerns grew among public health officials about the possible health risks associated with WW irrigation and other non-potable uses of RW. This concern led to the establishment of guidelines and regulations to control the use of WW for agricultural irrigation.

With the understanding that WW could be used as an important and safe soil fertilizer and that, at the same time, it posed serious risks of contamination, the practice had to be regulated. In this context, the state of California published its first regulation on water reuse in 1918. This is the first law regulating the use of WW in the Contemporary Age that is known in the world (Santos et al., 2022). According to Olivieri et al. (2020), the evolution of water reuse regulation in California followed the path shown in Table 2.

The evolution of water reuse regulation in California shows the important steps that have been taken toward the valorization of WW in the region. Since the regulation of California in 1918, many other countries in the world have followed this example. As mentioned before, Israel introduced its first regulation in 1957 (Santos et al., 2022) and currently uses almost 90% of the country's treated WW, representing 40% of its water demand for irrigation (Marin et al., 2017).

Advances in terms of regulation did indeed happen throughout the 20th century; however, they were very limited to arid and semi-arid regions with experiences of more severe droughts. As shown in Table 2, it is observed that in the second half of the 20th century, the concern about the use of WW in the production of edible crops increased.

In this period, in Europe, according to data available at the Musée des Égouts (Paris), in 1948, one-tenth of the vegetables sold in Les Halles in Paris came from sewage farms. However, the procedure was no longer as popular as usual, due to the following reasons: (i) excess WW; (ii) logistical complexity due to the natural seasonality of irrigation; (iii) biological treatment for disposal was gaining more popularity; (iv) new industrial fertilizers helped increase crop yields and competed with urban (sewage) fertilizers; and (v) with suburbs becoming more densely populated, less and less space was given to sewage farms. As highlighted earlier, the 20th century was marked by the decline of sewage farms.

Currently, due to climate change, the widespread pollution of water bodies, and the increase in population, there is a growing interest in the use of treated WW as an alternative source for water consumption. Yet better than saying an ‘alternative source’, we should say an ‘alternative and sustainable water source.’

However, the ‘Yuck Factor’ remains an unsolved problem. On the contrary, it is seen as one of the main challenges for the institutionalization of water reuse worldwide (Angelakis et al., 2018; Salgot & Folch, 2018; Santos et al., 2022). It is possible to imagine that during the period of WW valorization in ancient times, the acceptance of the practice was high. In reality, the practice was accepted due to a complete lack of knowledge regarding the pathogenicity of WW.

This lack of knowledge among users can be a determining factor in its acceptance. In Namibia, this was the main reason for the non-rejection of direct potable reuse (Fielding et al., 2019). A similar situation can be observed, in general, in relation to de facto (unplanned) indirect potable reuse (Angelakis et al., 2018). Users of water supply systems are generally unaware of the source of the water that supplies them. Therefore, they do not suspect its quality, even if the water source presents high levels of pollution due to the discharge of WW upstream.

On the other hand, water scarcity is the main driver of acceptance, according to Duong & Saphores (2015). In this case, users prefer to be supplied by an unconventional source rather than having their water supply interrupted due to scarcity. At this moment, utilities should enhance their awareness campaigns.

Another relevant issue for achieving success in accepting the practice of water reuse is the massive involvement of the government. Campaigns involving public figures lead to greater trustworthiness. This was the case with NEWater in Singapore when it was introduced to the public in 2003. As a persuasive strategy, the prime minister, ministers, and all members of parliament from the ruling party drank a bottle of NEWater during their official duties and public appearances. As a result, the acceptance rate was 98% among survey respondents, with 82% trusting direct use and only 16% relying on indirect use (Guan & Toh, 2012).

In the contemporary period, the 20th century was marked by the development of the legal-administrative basis for the safe use of WW as a source for water and fertilizers. The 21st century, on the other hand, has been highlighted by technological advances and by the different scenarios that require better quality water.

Now, it is necessary to concentrate efforts on awareness-raising actions, in addition to technological development and achieving legal-administrative security. This could be the path to a new era for water reuse in the 21st century. Thus, a transparent approach with user communities is needed, in addition to the implementation of pilot projects to instill confidence between the producer and the user of this new water.

The aforementioned factors led to the application of the practice for more noble uses, and even in the driest regions of the planet. Potable use, direct or indirect, requires advanced treatment technologies, appropriate regulatory framework, complex logistics of water resource management, more assertive decision-making, and a more engaged and participant society.

Some countries in the world already practice indirect potable reuse in an institutionalized way, such as the United States, Australia, Singapore, England, Belgium. Only the United States, Namibia, and South Africa practice direct potable reuse, for reasons of absolute necessity. Their treatment plants started operation between the late 1990s and early 2000s (Santos et al., 2022).

However, the uses that demand less restrictive water qualities, whose risks, and their contours are already widely known by science, have not yet advanced as they should, especially in the poorest regions of the world that suffer from water scarcity. Therefore, the first half of the 21st century may be the stage for this great transformation: it should produce more water for the necessary advances in sustainable socioeconomic development, and especially, to guarantee human dignity, with available water in the quantity and quality required for its various uses.

We can observe behavior of society in relation to the triad valuation x devaluation x revaluation of WW throughout our history. The understanding of the concept ‘VxDxR/WW Historical Development’ is of great relevance for the guidance of public policies, regional strategic planning, and the production of social instruments of education to achieve the acceptance of such practices.

For most of the history of society's development, the understanding of the benefits of waste for the fertilization of fields prevailed. This understanding must be resumed in the face of current society, in order to contribute to the acceptance of water reuse and to its institutionalization as a safe and responsible practice. Throughout history, the WW valorization period is much longer than the devaluation period.

The first 3,500 years from antiquity to the Roman period and the first half of the Modern Age were characterized by the valorization of WW. However, with the emergence of epidemics and the acceptance of the Microbial Theory, society started to connect WW (and pathogenic microorganisms contained therein) to the proliferation of diseases. At this point, the period of devaluation of WW begins, which lasted approximately 150 years, until the beginning of the contemporary period. In the last 100 years, since the beginning of the Contemporary Age, there has been an attempt to revalue the WW, with scientific, legal, and technological advances. These advances may make the first half of the 21st century an important stage for the dissemination of technical-scientific knowledge for the recovery of the value of WW.

A true paradigm shift is needed to guide appropriate decision-making that allows and encourages advances. In this sense, water circularity, with its economic, environmental, technological, social, institutional, and political factors, must be taken as the basis of actions to define appropriate public policies, in the context of efficient water management. These policies must follow paths for structuring regulatory frameworks appropriate to different regional characteristics, in order to guarantee a safe, responsible, sustainable and economically viable water reuse practice.

Finally, it is understood that the valorization of WW began with observation; devaluation as an effect of the Industrial Revolution and the spread of diseases; and revaluation as a consequence of droughts and more recently the drive of climate change. In the 21st century, it is necessary to concentrate efforts to achieve public acceptance, in addition to investing in technology and regulatory frameworks.

All relevant data are included in the paper or its Supplementary Information.

The authors declare there is no conflict.