I was alarmed the first time I saw water pouring out of what looked like a sewer grate and onto the road. Now, I watch for such a sight. It is another manifestation of the enlightened engineering, design, and vision that make Paris civilized. After all, the word city comes from the same root as civilized.

This photo tells part of the story of how Paris streets are cleaned. Water under relatively low pressure is emerging from a curbside opening, of which part of the cover is on the sidewalk. These are called WOs (washing outlets) or, in French, bouches de lavage, and there are 12,000 of them in Paris. In most cases, an old piece of carpet diverts the water from the road. The idea is to keep the water in the gutter where the sidewalk curb meets the road, so it can collect assorted debris and flush it into the sewer system.

Paris is also about style, fashion, and colour. So in the photo below red and green carpets add a little panache to engineering function. Notice the larger of the two holes on the checked cover plate inset into the sidewalk. That is where workmen insert a special wrench to turn the water valve to start or stop the flow of water.

In the photo below, we see that the piece of carpet is placed so that the water can go in one direction only. Any street debris will be carried along with the flow of water. In some cases the water flows undisturbed or unaided.

Paris’s men in green often give the water a helping hand. Here, on the rue du Faubourg St Jacques, near the Boulevard Port-Royal, water is flowing along the curb while two workers keep the debris moving where the tires of parked cars obstruct the flow.

Sometimes, as we see in the image below, there is a large amount of debris—after all, the Marché Port-Royal across the street had closed a short time ago—and it is skilfully and quickly swept together by the same two workmen. The larger pieces and clumps of leaves, paper, plastic and other rubbish go into the plastic bags in the cart. The rest will be swept away.

It is all part of an ingenious cycle. In the photo below, the blue carpet directs the water towards us and it flows down.

However, when one looks just behind the bit of carpet (upstream, so to speak), we see an open grate at road level. This is where the water from further upstream would bring its debris and re-enter the system. But this is no ordinary system, and Paris is one of the few cities in the world to have it.

How does it work? Why is it there?

Most cities have only one system to supply water, which is used for everything from making coffee, cooking, and taking a shower to cleaning streets, fighting fires, and watering gardens. Whether the water needs to be potable (safe to drink) or not, it all comes from the same place and the same set of supply pipes. We want our drinking and bathing water to be treated and purified, but it is expensive and energy-inefficient to have water for street cleaning or lawn-watering treated to the same standards as potable water. Nevertheless, that is what we do in virtually every city in the world. Well, not every city. Not in Paris.

In Paris, there are two different sets of underground water pipes. Both are attached to the ceilings of the sewers. One supplies untreated water for tasks such as flushing the streets of Paris. One system and set of water pipes carries untreated (non-potable) water from the Ourcq Canal and the Seine. The water comes out at various places through WOs on the curbs and after cleaning the streets and gutters, flows into the underground sewers. This water is then treated and discharged into the Seine. There is a parallel but separate system to deliver potable water to buildings, residences, homes, stores, and restaurants.

In other words, there are two water supply systems, each serving different purposes and each having varying purity levels. There is no mixing of water from the two systems, so don’t worry when you drink Paris tap water; it is safe and I like the taste. If you want to know more about the Paris Water Supply visit Le Pavillon de l’eau (Paris has got to be one of the only cities with an entire museum devoted to its water and water supply).

The Paris dual water supply system makes good sense. But it works only because it was part of the original plan for radical modernization of the city in the mid-nineteenth century. It would be too difficult to retrofit most modern cities to the same standard.

For this, we have to thank several people: Napoleon Bonaparte, the Emperor Napoleon III, Baron Haussmann, and a brilliant engineer called Eugène Belgrand.

Napoleon Bonaparte gave Parisians their first abundant supply of flowing water when he diverted the river Ourcq into the Seine within Paris. This is now known as the Ourcq canal.

Emperor Napoleon III (shown above) decided that for his greater glory and the greater comfort, convenience, and future fame of Paris, he had to modernize it, getting rid of many narrow crooked streets, opening up wide boulevards, and providing it with up-to-date infrastructure.

Carrying out this massive job fell to Baron Haussmann, who in turn chose Eugène Belgrand, a graduate of the world-renowned École Polytechnique, as his Director of Water and Sewers of Paris. Before Belgrand, Paris had had a massive, smelly, and not very satisfactory sewer and water supply system.

Belgrand made the sewage system four times larger than it had been before and when he finished, it was a tourist attraction. He doubled the amount of daily water available to each resident, while the number of dwellings with running water grew by four times.

It was Belgrand who put in the system that separated water for human consumption and water for other purposes. At a time when most water—drinking or otherwise—was not very good, it was an astoundingly far-sighted move. The initial costs were far higher than they would have been for a single system—the system most of the rest of the world has.

The river Ourcq water became the low-pressure non-potable system for what was called “public water” and the new high-pressure water drawn from underground became the “new waters,” a potable source under enough pressure to rise up to the top of the growing number of apartment buildings. Hence the famous signs proclaiming “Eau et Gaz à Tous les Etages.”*

That decision to have a dual water system and its execution keeps Paris streets clean today. And it involves more than water gushing out from a gutter drain and men with green plastic brooms helping it and the debris along.

One morning, as I sat on the balcony of our borrowed apartment, sipping coffee made with good Paris tap water and reading a book on nineteenth-century typewriter design, I quietly gave thanks for the men below who were working to keep the city so clean. One man drove the truck, while another swept the sidewalks with a high-pressure hose. Look at the front of the truck, with its system for spraying water from the movable front-mounted spray units.

The system is not only clean, it is energy-efficient. The truck is filled with untreated water, the kind of water that most cities in the world cannot reuse. The Velib’s are not the only thing in this picture to lower the carbon footprint of Paris.

If this photo represents part of what draws you to Paris, remember that only a minute later, I took this photo.

Thank you, Napoleon Bonaparte, Napoleon III, and the often-maligned Baron who carved the future out of the past and I think did a good job of a difficult task. And thank you also, Monsieur Belgrand. I intend to learn more about you. The city we love is built on the unglamorous but essential workings of its water systems, which were far more efficient than any others. This is just one of the many pieces of infrastructure that makes Paris so livable and, might I say, loveable. Paris’s dual water system is just as much a part of the Technology of Tourism as the Eiffel Tower.

Text and photographs by Norman Ball

*For a good introduction to the changes of Napoleon III and Baron Haussmann follow this link.