Eugène Belgrand & the water of Paris

I had only been living in Paris for a few weeks when I noticed an unusual phenomenon. The street gutters throughout my neighbourhood regularly flooded with water from valves in the pavement. At first, I assumed these to be leaks, but the frequency and regularity of the sight convinced me that it must be some kind of system for street cleaning. Baffled and concerned, I couldn’t envision how any 21st-century city could justify wasting water on this scale.

Rather than call my local Mairie in outrage, I did what I always do when I find something baffling. I went to the library. Once there, I made mention of the wastefulness of the street-cleaning system and the librarian took me to task. “Mais, pas du tout! Les égouts, ils sont la genie du Belgrand! Et Belgrand, il a bien pensé à tout.” Belgrand being Eugène Belgrand, who trained as an engineer at École Polytechnique and was Georges-Eugène Haussmann’s Director of Water and Sewers during the Parisian renovations of 1853-1870. The librarian didn’t elaborate, but given that the sewers seemed to be the key to unlocking the mystery of the street-cleaning system, I left the library armed with a few books on the history of Paris’s sanitation and a determination to better understand the city’s water system.

Although many large cities have interesting, often forgotten or hidden features beneath them, the strata of Paris’s underground is particularly rich. There are Roman-era archaeological remains, hidden medieval crypts, and Nazi bomb shelters. Having spent the best part of a year researching the history of limestone quarries beneath the city which were used for centuries in above-ground construction, I can say from experience that these quarries alone would be enough to give the city top marks for underground interest. But, perhaps the most splendid underground world in Paris is the one linked to its water system.

One cannot hope to understand the Parisian water system without first understanding its infrastructure. The 2,000km of underground water pipes threaded throughout Paris’s sewers are mirrored above ground by 470km of aqueducts which bring water from neighbouring départements to the capital. Both the aqueducts and the pipes are in turn connected to numerous water-treatment facilities and storage reservoirs, which today supply water to 3.5 million residents, commuters and tourists. The complexity of the entire system is testament to Belgrand’s foresight and ingenuity. If Haussmann’s name is widely known outside France for his role in reshaping Paris, Belgrand’s is virtually unknown, even though it was arguably only thanks to Belgrand’s ambitious new sewers and aqueducts that Haussmann’s transformative plan was possible.

Prior to 1850, the city’s main source of drinking water was the river Seine, which was also the principle location for the discharge of waste water. Given the 19th century’s five-fold population increase in Paris, such arrangements unsurprisingly resulted in considerable health problems linked to water sanitation. The devastating cholera epidemics of 1832-35 and 1848-49 had not only killed thousands of people, but, by the time Haussmann became prefect in 1853, had also come to influence strategies for urban planning. Arguments for wider streets and sidewalks – as well as the necessity of a proper sewage system – were direct results of 19th-century cholera outbreaks. Thus, a major component of Belgrand’s brief was to develop a new sanitation system, one which would provide and maintain a clean water source to reduce related health epidemics. As Haussmann wrote in 1854, “these subterranean galleries, organs of our great city, would function invisibly, like those of a human body. Pure, fresh water, light and heat would circulate like those various fluids whose movement and maintenance sustain life. Such separations would mysteriously maintain public health without disturbing the order or exterior beauty of the city.”

Belgrand’s solution was manifold, encompassing drinking and non-drinking water networks as well as wastewater disposal. Although the Seine was then too polluted to supply clean drinking water, in observing that Paris required water for additional uses – watering public gardens, fighting fires, cleaning streets – Belgrand reasoned that the Seine could continue to serve a non-potable system at a much lower cost. For drinking water, Belgrand looked to non-contaminated sources further afield. Where today many American cities continue to water their lawns and wash their cars with expensively-treated drinking water, Paris instead adopted Belgrand’s dual-network system which continues to this day. Construction of the new sewers began in the 1850s and by 1878 some 600km of tunnels had been excavated. In 1800, by way of comparison, the city had a mere 25km of sewers for 700,000 inhabitants.

Above ground, Belgrand worked towards the creation of a new network of aqueducts to bring clean drinking water into Paris from natural sources outside of the capital. These new resources brought drastic improvements, doubling the amount of water available for each individual resident and bringing running water into almost four times the number of homes. One perhaps surprising feature of Belgrand’s new system was his commitment to aesthetics. Much of the sewer system designed under his care is surprisingly elegant –even the drawings themselves are beautiful. Having visited Belgrand’s Aqueduc de la Vanne (constructed between 1866 and 1874) where it traverses the Fontainebleau Forrest, the sophistication and decorative detailing of this massive piece of infrastructure, situated effectively in the middle of nowhere, seems surprising. But both Haussmann and Belgrand had at their disposal the extensive resources and innovative debt financing of Louis-Napoléon Bonaparte, not to mention the prestige and reputation of the Second French Empire at stake.


When I pour myself a glass of water from the tap in my apartment, between the ground water at source and its subsequent arrival at my tap, the water must first be treated. The 20 arrondissements of Paris are split into four catchment areas, each with one or two unique water sources in different locations in Île-de-France, Bourgogne, Normandy, or the Seine and Marne rivers. These catchment areas are then coupled with five water reservoirs, three of which are inside the city, two just outside at Saint-Cloud and L’Haÿ-les-Roses.

The tap water that ultimately makes its way to my flat in the 7th arrondissement begins its journey as source ground water from the Voulzie River near Provins and the River Loing, south of Fontainebleau. Water from the Voulzie is treated at a plant in Longueville before being sent to Paris via the Aqueduc de la Voulzie, which feeds into the Aqueduc de la Vanne. Similarly, water from the Loing is treated at a plant in Sorques before being sent to Paris via the Aqueduc du Loing. The water from both aqueducts travels towards the capital, stopping first for treatment and testing at the L’Haÿ-les-Roses factory before then being sent to the Montsouris reservoir, a spectacular structure in the 14th arrondissement, designed by Belgrand and opened in 1873.

Constructed on top of reinforced ancient limestone quarries, Montsouris has a storage capacity of 202,000 cubic metres of water, representing approximately a third of the city’s daily consumption. As with the aqueducts, Belgrand’s reservoirs are surprisingly beautiful buildings. From the street, Montsouris looks rather imposing: a high millstone wall runs nearly 300m along the Avenue Reille and is topped by two glass and metal pavilions. Although the pavilions, more commonly known as “lanterns”, have the appearance of surveillance towers, they house the reservoir’s famous “tulips”, three vertical pipes which flow the water into the reservoir after its three-day journey along the aqueducts. Thus, the pavilions are elevated in order to maintain pressure and ensure the necessary slope for the flow of water. Indeed, Belgrand’s system, inspired by his own careful studies of Roman engineering, means that, even today, drinking water is conveyed to Paris without electricity, using only the force of gravity.

From the Montsouris, or any of the other four reservoirs, drinking water is then carried across the city through pipes fitted inside the 2,000km of sewer tunnels. The city’s drinking-water system stops at the point of entry – each apartment building or office block is responsible for its internal pipe work – but then picks up again at the point of exit in its waste water system. So too with the aqueducts, much of Paris’ wastewater flows into the sewers and towards the main treatment plant in Clichy via gravity, thanks to the natural incline of the Paris basin.

Although water-treatment technology has modernised considerably since the mid-nineteenth century, the utility of Belgrand’s infrastructure is undiminished. Belgrand’s nineteenth-century dual-network system has allowed twenty-first century Paris to use more-expensive treated water for drinking and cheaper, untreated water for necessary municipal functions. The water rushing along the street gutters I observed in my first weeks in Paris is drawn from this secondary system. Non-potable water is collected from the Seine and the Ourcq Canal and subjected to a simple screening process to remove large bits of matter before being stored in various non-drinking water reservoirs, such as the large Passy Reservoir in the fashionable 16th arrondissement, constructed between 1858 and 1866. When this non-potable water is returned to the sewers, as it is in street-cleaning uses, it joins the sanitary wastewater sent to the Achères treatment plant (first operational in 1940), today one of the largest in Europe. Here, wastewater is nitrogen treated and biofiltered before ultimately being returned again to the Seine.

The smell of a Parisian sewer is, as you might expect, overwhelmingly pungent. Since at least 1867, when the first public tours were offered, the sewers have attracted tourists. “The majestic sewers of Paris have always been a source of public fascination and have been honoured by the most illustrious visitors,” Belgrand wrote with pride in 1887. “Not one foreign monarch or eminent person has left Paris without visiting the sewers.” From 1892 to 1920, visitors rode through the sewers in a locomotive-drawn wagon. In 1920 the wagon was replaced with a boat, which floated tourists along the canals until 1975. Today, the curious can visit a small section of the sewers in the little-known Musée des Égouts de Paris, not far from the Eiffel Tower. It’s only really here, among the sewers themselves, that one can truly begin to appreciate the scale of Belgrand’s vision.

Many of tunnels that make up the Paris sewer system are very large, almost the size of a metro tunnel. In several locations a central channel, wide enough and deep enough for a boat, carries waste and runoff water; broad, paved walkways sit on both sides, with enough headroom for workers to walk comfortably. Overhead are pipes that supply the city’s fresh water in addition to telecommunications cables, pneumatic tubes and the electrical system for traffic lights. In other places, the tunnels are a tight squeeze for the workers who visit to monitor leaks and ensure that water flows freely. As above, so below, and the tunnels underneath the city almost precisely mirror the layout of the streets above. Every corner within the sewers boasts an identical street sign to its surface-level companion above. Where a wide boulevard runs on the surface, a wide sewer runs below. Smaller streets have smaller sewers, likewise side streets and alleys. It is the size, scale and multi-purpose quality of this mirrored network that contrasts Paris’ sewer system with many other world cities.

Equally impressive are the curious tools that Belgrand and his team of engineers designed for ensuring the sewers remained operationally stable. There’s the bateau-vanne, a flat-bottomed dredge boat weighing in around five tonnes which floats down the canals to ensure that the weight of solid material doesn’t clog up the sewers. There are also the astonishing boules de curage, enormous iron and wood balls which are almost precisely the same diameter as the sewer tunnels. When a build-up occurs in any given tunnel, one of these heavy balls is be dropped in the sewer and hurtled through, clearing any debris in its path. Remarkably, nearly 170 years later, the barge and cleaning balls are still used today by Parisian sewer workers.

If certain of Paris’s underground worlds are comparatively ignored in the popular imagination – the historic quarries or the networks of metro tunnels – the same cannot be said for the sewers. Victor Hugo dedicated nearly 50 pages of his 1862 Les Misérables to a thorough description of Paris’s sewers told through the adventures of parole-breaker Jean Valjean. Among other cultural creations, the city’s sewers have also played a starring role in Phantom of the Opera and more recently, the Disney film Ratatouille.

Perhaps it is these long-held cultural associations – between the sewers and law-breakers or the sewers and rats – which have contributed to the peculiar relationship Parisians have with their tap water. Despite current statistics which hold that 88 per cent of Parisians have confidence in the quality of their tap water, the city’s denizens (and the French in general) are among Europe’s biggest consumers of bottled water (France’s annual consumption rate is 122 litres per person, ranking fifth after only Italy, Germany, Hungary and Belgium). Bottled mineral water is bought in large quantities for domestic use and café tables across the city are littered with Perrier bottles. Unsurprisingly, France’s bottled water companies have helped to play their part in maintaining the common perception that Paris’s tap water isn’t fit for drinking. In 2015, the city’s water company, Eau de Paris, won a lawsuit against Cristaline water, after an aggressive 2007 advertising campaign declared that Paris’s tap water contained nitrates and lead, wasn’t safe to drink, and came directly from toilets. “Unfortunately, it’s a common perception and we work diligently to change that,” says Benjamin Gestin, who is the managing director of Eau de Paris. “Paris also has many first-generation immigrants who come from countries where tap water isn’t safe and they bring this assumption with them here to Paris. We work hard to change these perceptions but it takes time.”

More recently, if anything has been working towards changing the city’s inhabitants’ perception of their drinking water, it has been the status of Eau de Paris itself. After nearly 25 years of private management, the city’s water supply was returned to public management in 2010. In 2008, the former Paris mayor Bertrand Delanoë had run his re-election campaign in part on a platform of re-municipalisation of the water system. The timing was fortuitous, given that the two principal private management contracts for the system were coming up for renewal. Rather than renew, Delanoë brought the entire system back under public control. “The main factor which prompted re-municipalisation was a lack of fiscal transparency,” says Gestin. “The service was good, but it was expensive and getting more expensive every year at a steady rate.” Since re-municipalisation, the city’s water prices have stabilised and company profits are reinvested back into the system with an eye towards future generations. “One of the first things people mention as a virtue of public management is price,” says Gestin. “And that’s true, the price of water in 2017 is cheaper than it was in 2010, but the real strength of public management is its capacity to work on a longer term. I don’t need to give money back to shareholders in the next five years. My objectives are for 2030, not 2019.”

Given current Paris mayor Anne Hidalgo’s outspoken leadership on climate change and sustainable development, the city’s water supply understandably plays an important part in its long-term environmental strategy to become completely carbon neutral by 2050. The broader environmental strategy of Eau de Paris is above all to protect the natural water sources which provide water to the city, to maintain and increase biodiversity, and to control its own energy consumption in water processing. Following re-municipalisation, for example, Eau de Paris has been working closely with 140 farmers in the catchment areas from where its drinking water is sourced to encourage the reduction of agricultural chemicals or even wholesale conversion to organic practices. “Helping these farmers reduce or eliminate pesticides costs three times less than the post-processing of water in the plant,” explains Célia Blauel, the deputy mayor of Paris charged with water. “Today, 80 per cent of our groundwater is polluted. This is a major environmental and economic issue.”

As far as the utility’s day-to-day activities are concerned, a major environmental focus is to preserve water through two strategic goals: encouraging control of user consumption and improving network efficiency. “My financial interest as the GM of Eau de Paris is to encourage Parisians to use as much water as possible and then bill them,” says Gestin. “But instead we recognise that water is a vital public service and we try to educate Parisians as to its conservation.” A graph of Paris’s water consumption from 1945 to 2010 shows an increase from 140 million cubic metres per year to a high point of 250 million cubic metres in 1990, followed by a gradual, if surprising, subsequent decline. Gestin explains that declining consumption has been caused by the general stabilisation of the city’s population, the effects of Airbnb and other short-term holiday lets on demand (a recent report held that some 30 per cent of properties in the 1st to 4th arrondissements are largely empty year-round), and the decline of large industry within the Périphérique.

Network efficiency on the other hand attempts to ensure that, for each drop of water taken from the natural environment, as much as possible is distributed within the Parisian system. The current system efficiency rates at 90 per cent, compared to the national average of 80 per cent, and Eau de Paris is constantly seeking methods for improving this percentage. In-development methods for leak detection, for example, include acoustic detectors which are able to determine the precise location of leaks in the system thanks to the sonority of its 19th-century iron pipes. Experiments are also ongoing in which drones could be used to detect and source leaks, and even possibly repair them, again with a view to improving overall network efficiency. For Gestin, an added bonus of such efficiency improvements would be the reduced need for workers to enter into the sewers for relatively trivial tasks. “It’s a very difficult job to work down there,” says Gestin. “One of my chief priorities as General Manager is to reduce, if not eliminate, the need for manual labour in the sewers.”

Although cutting-edge technology increasingly plays a part in the supply, monitoring and maintenance of drinking and non-drinking water, the beating heart of the network remains Belgrand’s 19th-century system – a system which Eau de Paris feels duty-bound to preserve. “In many ways, a system inherited from visionaries is the best system we could design today. We couldn’t really do it better,” Gestin says. “We have been able to modernise the system and preserve it, in part because it’s our moral duty to preserve our heritage, but the inherited system has also set a quality standard which we feel we much match.” In this, Gestin refers to not only the preservation and the maintenance of Belgrand’s sewer system, but also the architectural ambition of his infrastructure, his grand aqueducts and reservoirs. When, for example, a drinking-water treatment plant in Ivry-sur-Seine, in the south-eastern suburbs of Paris, was closed down and rebuilt from 1987 – 1993, an architectural competition was held for the new building’s design – a competition won by the celebrated French architect Dominique Perrault.

Belgrand’s water network is being updated and future-proofed in other surprising ways, too. Amidst chaotic housing developments by Philéas K Architecte and MAD in a new, 500,000-square-metre development in the 17th arrondissement, a cutting-edge geo-thermal plant has been integrated into the Clichy-Batignolles “écoquartier”. Partnering with the City of Paris and Compagnie Parisienne de Chauffage Urbain, a local heating provider, Eau de Paris has drilled deep-water wells as an emergency back-up system – life-saving resources should the entire main network collapse. As the water in these deep wells is at a relatively high temperature, 28°C, these emergency reserves also providing heating to 83 per cent of the new development through an on-site geothermal plant. Similar future developments are being planned elsewhere in Paris, but the appearance of large-scale geothermal projects is a strong sign that Hidalgo’s commitment to renewable energies and carbon reduction is being matched in practice, as least as far as the city’s water supply is concerned. Fluctuat nec mergitur, as the city’s watery motto holds: battered by the waves, but never sunk.

This story originally published in Disegno #17.

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