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About the Author
David Sedlak is the Malozemoff Professor in the Department of of Civil and Environmental Engineering at the University of California, Berkeley, co-director of the Berkeley Water Center, and deputy director of the National Science Foundation’s engineering research center for Reinventing the Nation’s Urban Water Infrastructure (ReNUWIt). He is the 2014 recipient of the National Water Research Institute Clarke Prize.
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The Past, Present, and Future of the World's Most Vital Resource
By David Sedlak
Yale UNIVERSITY PRESSCopyright © 2014 David Sedlak
All rights reserved.
Water Supply in Rome, the World's First Metropolis
If water is the essential ingredient of life, then water supply is the essential ingredient of civilization. In ancient times, when people first began gathering in settlements for trade and mutual protection, they tended to locate within a short distance of their drinking water. But as settlements grew into villages and villages gave way to cities, people were forced to live farther away from their water source. Initially, the challenge of supplying areas of the city that were far from water was solved by digging a well or by paying for home delivery of water. For the inhabitants of the first cities, obtaining water was just one more challenge that had to be overcome to reap the benefits of urban living.
As time passed, cities experimented with ways to import water. For example, around 700 BCE, inhabitants of the city of Erbil, in northern Iraq, dug gently sloping horizontal tunnels known as qanats to route groundwater into the city from a distance of approximately twenty kilometers (twelve miles) away. Around the same time, the Greeks dug shallow canals to divert water into Troy and Athens from springs in the nearby hills.
Densely packed groups of houses and the compressed soils that made up city streets also required drainage systems to prevent flooding. Early civilizations in the Indus Valley and Mesopotamia developed elaborate systems of gutters and covered channels for directing any water that accumulated in the streets into the nearest waterway. In many cases, the drainage systems included a way to collect drinking water: cisterns were built to capture clean water that ran off the roofs of buildings.
These early prototypes made it clear that there were technological solutions to each of the major problems of urban water supply and drainage. But credit for the development of Water 1.0—a complete system of importing water, distributing it to homes and public spaces through a network of pipes, and returning used water to the environment—goes to the ancient Romans.
When it came time to take water to the next level, Roman water engineers didn't really have a choice: their city's water demand grew too big for the local sources. Before the Romans, the biggest cities in the ancient world rarely had more than 100,000 people. Provided that the climate was not too arid and the geology didn't preclude the use of shallow wells, cities of this size could usually manage by using local sources of water. But Rome was different. By around 300 BCE, the city's population had grown to somewhere around half a million people who not only needed to drink, but also loved baths and other forms of water recreation. After Roman society began to thrive, the Tiber River (which runs through Rome), the shallow groundwater, and the local springs were no longer able to meet the needs of the thirsty city. In response, over the next five hundred years the city's engineers built a water system that ultimately imported enough water to supply Rome with a daily allotment comparable to that of our modern cities.
When someone mentions ancient Rome's water supply, what first comes to mind are the graceful arches and elevated structures that crossed the arid valleys leading to the city. The iconic bridges, arcades, and viaducts of Rome are remarkable examples of the advances that Roman engineers made in structural engineering, hydraulics, and surveying. They also exemplify Rome's ability to create durable structures with concrete and masonry. Yet the graceful, elevated sections of the aqueduct, while essential to the transport of water over long distances, are just a small part of the story: they made up only around 5 percent of the length of Rome's imported water system. Furthermore, the Romans tried to avoid building them whenever possible, because they were costly and prone to failure. For example, the elevated section of the Aqua Claudia aqueduct took fifteen years to build and during its first two de cades of use was only in ser vice about half the time. Elevated structures were weak links in the Roman water supply chain. If the topography around the city had been more favorable, the Roman engineers would have avoided them entirely.
Most of Rome's aqueducts actually consist of canals or underground pipes and tunnels that were made from masonry or cut into rock (the word aqueduct is derived from aqua—"water"—and ductus, "enclosed passage"). Although the entire Roman water system worked by gravity, maintenance of the reservoirs and aqueducts required vigilance so that damaged pipes and tunnels would be fixed quickly and debris that could block the low of water would be removed. All of this maintenance and the construction of new aqueducts to meet the city's growing water demands required both funding from the emperor and donations by private citizens.
Outside the city, much of the imported water system was hidden from view. The citizens of Rome could only see what their money had bought when the imported water entered the city on elevated structures, but these reminders of the infrastructure investment could get lost in the bustle of the city. To make the people aware of their accomplishments, Rome's leaders decorated the arches of the arcades where the aqueducts entered the city and built ornate fountains in public squares. All of this extra effort can be seen as a political statement about the good works that the government had done rather than a tribute to the gods or an altruistic attempt to beautify the city. When Rome's aqueducts were rebuilt at the start of the Renaissance, the popes made sure that these decorative fountains were restored and updated for many of the same reasons.
In contrast to the Roman practice of building monuments to increase awareness of the city's hydraulic assets, most water arrives in modern cities with little fanfare. When fountains are built in public spaces, they are more likely to commemorate some nearly forgotten historical event or a deceased political figure than they are to celebrate the engineering prowess or institutional organization that was required to make the water low. Perhaps if our water utilities took a cue from the Romans and advertised their accomplishments with beautiful fountains, they would have an easier time convincing the public about the need to invest in the upkeep of the system.
The aqueducts behind the fountains truly are engineering marvels when you consider that the Romans—without the aid of backhoes, concrete mixers, or satellite-enhanced surveying systems—built tunnels to exacting tolerances that followed the natural slopes of the hillsides. Placing the water supply underground avoided many of the challenges posed by viaducts. It also made the system more difficult for enemies to sabotage and minimized the likelihood that the water would be polluted as it lowed into the city.
Although the operation of a gravity-fed underground water delivery system may seem like a straightforward task, the Romans had to resolve a number of difficult problems in their quest to create a system that could reliably deliver water. Over a period of trial and error that spanned five centuries, the ancient Romans came up with concrete that could cure when exposed to water, arches capable of bearing the weight of massive volumes of water, and a number of other useful inventions. For example, some sections of the aqueduct had to go down steep hills. Water lowing along these sections would move so fast that it would erode away the channel. The Romans solved this problem by installing stone structures in the aqueduct that made the bottom of the channel rough and so slowed the water's momentum.
When the aqueduct crossed through a valley, it was necessary to move it up the next hill without the use of mechanical pumps. Roman engineers solved this problem by building massive inverted siphons that used the following downstream section of the aqueduct to help pull the water over the hill. (If you have ever used a short length of garden hose to empty out an old aquarium or to take some gasoline out of your car's gas tank, you know how this works on a small scale: you fill the hose with water, or some other fluid, and as long as the place where the fluid leaves the hose is at a lower elevation, it will low up and out. The Roman inverted siphons worked this way, except their "tubes" were made of bundles of lead pipes, each twenty-five centimeters [ten inches] in diameter.)
Roman engineers also had to grapple with changing conditions at the water source. Sometimes the water that they wanted to route through the aqueduct contained clay and sand that had been stirred up by a recent storm. If they let the sediment-laden water into the water distribution pipes, the pipes might clog. The Romans solved this problem by building wide troughs within the aqueduct system where the water velocity would slow enough to cause the particles to settle out (like sand in a lazy river) and where these particles could be removed easily by maintenance crews.
Springs and streams located in the hills around the city fed the aqueducts and in most cases were easily connected to the water supply system. Sometimes, however, more complex engineering was employed. For example, the Anio Novus Aqueduct took its water from a reservoir that had originally been built to create a lake at Emperor Nero's villa. The forty-meter-high (130-foot) dam that held back the river remained the highest dam in the world for 1,500 years.
A total of eleven aqueducts, with a cumulative length of over four hundred kilometers (250 miles), were built as Rome's water demand grew. The Romans developed considerable expertise during the expansion of their water supply, because each successive project posed new and more difficult challenges. The knowledge that the Romans accrued while constructing their imported water systems allowed them to act as the world's first multinational construction company as they spread Water 1.0 to far-lung parts of the empire.
Ultimately, the aqueducts brought water into their capitol from distances as far away as approximately eighty kilometers (fifty miles). On a map of ancient Rome's aqueduct system, you can see the pattern that would later be repeated in the imported water systems of cities like Paris, New York, and Los Angeles: as the population needing water grew, the water system's canals extended ever farther from the city center, much like the ever-expanding root system of a growing plant.
Delivery of imported water to the fountains was quite a feat, but it solved only part of the problem. Because there were advantages to living close to the heart of the city, Rome experienced the same housing pressures that we encounter in cities today. That is, as its population density increased, detached housing became a luxury reserved for the privileged class. For the average Roman, home was an apartment in a building three to six stories high, and because Roman tenements weren't equipped with indoor plumbing, water had to be lugged upstairs. It isn't much of a surprise, then, that most Roman water use happened at street level.
In contrast to the masses, rich and inluential Romans oft en had water piped directly into their homes, to a small fountain in a central courtyard. But the right to have piped water required official permission that could be difficult to secure. As a result, the rich oft en bribed local officials or surreptitiously connected their homes to the public water supply. In a survey of water use, Frontinus, the Roman water commissioner who served at the end of the first century CE, complained about the practice of "puncturing" the water system by making illegal connections. He wasn't certain how many illegal connections had been made in Rome, but he assumed that the practice was pervasive because of the large numbers of illegal pipes his workers had discovered as they repaired the streets.
The fountains and water pipes that conveyed the water into Roman homes were made of lead, which seemed like a wonderful material for plumbing. Lead-containing ores are relatively easy to find, and lead is perfect for making into pipes because it melts at a low temperature and can be molded easily into all kinds of shapes. Unfortunately, lead is also a potent neurotoxin. The Roman engineer Vitruvius and his contemporaries were well aware of this problem and noted that lead pipes were unhealthy and should be avoided because they could cause water to "become corrupted." Even so, the Romans employed them everywhere because they were useful and convenient, and because there were few other choices for material from which to make pipes. Indeed, the word "plumbing" is derived from the Latin word for lead, plumbum, which also provides us with its abbreviation on the periodic table—Pb.
In the late 1970s, when scientists were becoming increasingly aware of the health hazards associated with leaded gasoline and lead pipes used in modern plumbing, a number of books and papers were written in which the fall of Rome was blamed on exposure to lead. Although this theory has not been embraced by classical scholars, who can identify many more viable explanations for the downfall of Rome, it is clear that the Romans were exposed to massive quantities of lead from sources unrelated to their water supply. The Romans used lead salts to sweeten their wine, and they cooked and stored acidic foods in lead-lined containers under conditions that would leach large quantities of lead.
The pipes that transported water around the city were another possible source of lead exposure for the ancient Romans. But when it came to water pipes, the Romans got lucky: the geology of the hills surrounding the city likely reduced the potential for lead to leach out of the water pipes. The region where the city's water supply was obtained had ample deposits of calcite—a relatively soluble mineral. The calcium present in the imported water appears to have precipitated inside the lead pipes, forming a protective mineral layer that prevented lead from leaching into the water. In fact, contemporary engineers take advantage of this phenomenon when they manage water distribution systems that contain lead pipes and lead-soldered plumbing. By increasing the pH of the water to encourage the development of protective mineral layers, they prevent the lead from leaching out of those old pipes and soldered joints that are too expensive to find and replace.
Once imported water was available, the Romans came up with all kinds of creative ways to use it. During the height of the empire, the Romans staged mock naval battles in which thousands of slaves reenacted historic fights, complete with real blood. One of the Roman aqueducts was even built mainly for filling up the artificial ponds used for the mock battles. It is notable that the Romans chose the water supply with the lowest-quality water for this purpose, saving the water sources with the lowest salt content and fewest suspended sediments for the fountains and private water supplies. Although we no longer stage mock naval battles, we still use lots of water to entertain ourselves at golf courses, parks, and swimming pools. As we'll see, the Roman practice of building a separate water supply system for uses where quality is not as critical is becoming an increasingly popular approach in places where modern water supplies are limited.
The Romans also were enthusiastic about bathing: Rome was packed with public baths with hot water supplied through a sophisticated system of heaters and plumbing. The baths were social centers that served various recreational purposes, much like modern-day health clubs. In addition to getting clean, you could meet up with your friends, attend a lecture, or get some exercise at the baths. The typical Roman washed every day and took baths almost as oft en, especially before festivals and public holidays.
There is considerable uncertainty about Roman water consumption, with estimates of daily per capita water use ranging from approximately 200 to 1,200 liters (50 to 300 gallons), depending on one's assumptions about how the aqueducts were operated. Whichever assumptions are correct, it is clear that Roman per capita water use was comparable to that of modern cities and far exceeded the amount needed for consumption and basic hygiene.
Because Rome's water supply relied on springs and streams whose low varied according to the season, the city received less water during dry periods. As a way of prioritizing the various uses of water during times of drought, the tank where water from the aqueduct entered the city, known as the castellum divisorium, was designed with separate outlet pipes for the public fountains, private homes, and baths. This configuration ensured that after a minimum amount of water entered each of the three water distribution systems, the excess would low to the public fountains where most people obtained their water, meaning that these public fountains would normally receive the largest water allocations. At Pompeii, the castellum divisorium had sluice gates that could be put in front of the pipes to cut off the low during a drought. Some modern cities also have set up priorities for water use during droughts, but we oft en rely on voluntary compliance or enlist utility employees and city workers to catch people who are illegally watering their lawns or washing their cars. If our modern water distribution systems prioritized among users as the Roman systems did, it would be a lot easier to ration water during droughts.
Excerpted from Water 4.0 by David Sedlak. Copyright © 2014 David Sedlak. Excerpted by permission of Yale UNIVERSITY PRESS.
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Table of Contents
1 Water Supply in Rome, the World's First Metropolis 1
2 The Bucket Era 14
3 Europe's Sewage Crisis 26
4 Growing Old Thanks to Water Treatment 41
5 Burning Rivers, Fading Paint, and the Clean Water Movement 63
6 The Chlorine Dilemma 90
7 "Drains to Bay" 112
8 Traces of Trouble: Hormones, Pharmaceuticals, and Toxic Chemicals 139
9 Paying for the Fourth Revolution 164
10 The Toilet-to-Tap Solution 187
11 Turning to the Sea for Drinking Water 217
12 A Different Tomorrow 238
13 Reflections 273