Every day, about 430 million gallons of water enter Los Angeles from the eastern slopes of the Sierra Nevada Mountains. The journey begins in the sky, when rain and snow fall on the mountainside; water then flows into the Owens River and travels a human-built route for the next 200-plus miles. Pipes, tunnels, and canals—all mapped out a century ago—navigate hills, valleys, and desert terrain en route to North America’s third-largest city.
Yet the most remarkable aspect of this system, the Los Angeles Aqueduct, might be its reliance on the most basic concept of drinking water engineering. Because the water comes from the mountains, the aqueduct is built on a downhill slope. To get to its destination, all the water needs is gravity.
Of all the water on the planet, only about 3 percent is fresh—that is, largely saltless and generally drinkable. Of that 3 percent, about two-thirds is frozen in the world’s melting glacial ice. The remainder lies underground and in lakes, rivers, ponds, and springs; it has sustained life on land for millennia.
“There are very few true universals in the human condition,” says James Salzman, the author of Drinking Water: A History. “But drinking safe water is one of them.”
Most of our ancestors lived nomadically, and in that lifestyle, finding a drink was as simple as filling a gourd on the side of a river. But as humans settled and societies expanded, crowding close to fresh water became impossible. That’s where the engineering history of drinking water truly begins, and it starts in the Neolithic Age.
Early societies developed several methods to meet the challenges of importing water. Canals, wells, and cisterns were prevalent thousands of years ago across the ancient world. In present-day Jordan, the first known dam was constructed of compacted earth and masonry to hold back water and sustain the city of Jawa.
Up through antiquity, no civilization dreamed bigger than Rome. In population alone, Rome was the first “modern” city, with an estimated one million people—at least 10 times more than almost any other ancient city. To supply its residents, the city’s engineers designed an infrastructure project on an unprecedented scale. From 312 BCE to 226 CE, they built 11 structures that delivered water from springs and lakes as far as 57 miles away. They called these life-giving structures aquae ductus, Latin for “water” and “conduit.”
The aqueducts operated almost entirely through pipes and tunnels built at a declining slope. To cross shallow valleys and maintain that gradient, the Romans created grand, arched bridges that became enduring symbols of their ingenuity. Where the land dropped too deeply to construct a bridge, they built a series of pipes that plunged down and rose back up the next hill at a slightly shorter elevation. This design allowed the water to fall from the higher position and maintain enough force to reach the shorter side. It also enabled the entire system to operate by gravity alone. This was two millennia before the planning of the Los Angeles Aqueduct.
“We think about the Roman water system as the archetype,” says David Sedlak, author of Water 4.0: The Past, Present, and Future of the World’s Most Vital Resource, “because it essentially established the model that all future water supplies would follow.”
When the water entered the city, it flowed to bathhouses and extravagant street fountains. With no faucets back then, the water ran continuously, and overflow cleaned the streets and drained into the city’s sewer system (a whole other engineering marvel).
As the empire declined in the 5th century, many of the aqueducts fell into disrepair. Some were restored during the Renaissance, and one of them—the Aqua Virgo, which the engineer Sextus Julius Frontinus meticulously documented at “14,105 paces” in length—still brings water to the Trevi Fountain. But it took more than a millennium before the world, pushed to the brink by deadly pandemics, improved on Rome’s hydrological genius.
Smelly Cities and Disease
The fall of the Roman Empire sent Europe into a tailspin of terrible sanitation that turned streets into dumps. For centuries, people threw garbage and the contents of their chamber pots out of their windows. Much of that waste seeped right into Europe’s wells and rivers, and in the 17th and 18th centuries, the Europeans brought their unsanitary practices across the Atlantic.
New York was notorious for its filth. In 1785, an observer for the New York Journal described people gathering by their drinking source, the long-gone Collect Pond, to scrub “things too nauseous to mention; all their sudds [sic] and filth are emptied into this pond, besides dead dogs, cats, etc. thrown in daily, and no doubt, many buckets [of excrement] from that quarter of the town.”
Pungent odors permeated New York and other cities in the early 19th century, and disease followed. In 1831 alone, more than 50,000 people in Great Britain died from typhoid fever. A year later, New York City recorded 3,500 deaths from cholera. The world, still decades away from understanding waterborne pathogens, blamed the smelly air.
New York’s leaders at least understood that their pond was repugnant and that it would never supply enough water to sustain a growing city. After years of surveying, they determined that the closest and most reliable source of clean water was outside Manhattan, flowing in the Croton River 40 miles north.
About 1,600 years had passed since Rome built its last aqueduct. Even after all those centuries, moving water over such a distance was a massive undertaking. The project’s chief engineer, John B. Jervis, designed an aqueduct emulating the ancient model, with a 55-foot-tall masonry dam and tunnels descending 13 inches per mile. To maintain that slope, thousands of workers blew up rock and carved straight through hills. When the aqueduct reached the city, it crossed the Harlem River over a 1,420-foot-long arched bridge inspired by the Roman aesthetic. The water then flowed into iron pipes underground and filled reservoirs and street hydrants with drinking water. When it opened in 1842, the Croton Aqueduct became the template for projects in Boston, Philadelphia, and other American cities, including Los Angeles decades later.
Within New York City itself, the water system could do something maybe even more extraordinary. Between the slope and the gravitational pull, the water accrued enough pressure to ascend into buildings as high as six stories. Over the next several decades, the city transformed its closets into rooms with toilets, sinks, and tubs. Running water had entered the home, revolutionizing the way we could fill a glass. As Manhattan grew taller, thousands of wooden towers sprang up across the city’s rooftops, where water was pumped for storage before trickling down, once again, by gravity.
This concept was replicated around the world. Most water towers, by design, are taller than the buildings surrounding them. Suppliers pump the water into this one structure, after which it drops down and then rises back up into shorter buildings.
As New York City’s population skyrocketed into the millions, the city expanded the Croton Aqueduct and built two more, each about 100 miles long, from the late 19th century through 1965. Together, the three aqueducts convey about 1.2 billion gallons of water to the city and to towns along the way—every single day. Almost all of that water has remained pristine, and persists as the largest unfiltered supply in the United States.
But New York is lucky—most cities don’t have such clean sources. Instead, they rely on filtration. That story begins with the solution for typhoid and cholera.
Cleaning Our Water
In 1829, London’s Chelsea Waterworks Company prototyped a filter designed to make the water from the city’s polluted Thames River look clearer and taste better. It comprised a layer of sand atop a bed of gravel, with a tank built underneath to capture the cleaned water that trickled through. After a few weeks of pouring water over the sand, a gooey biofilm formed on top. The biofilm did the trick—the water in the tank looked and tasted cleaner—but what the engineers didn’t know was that the biofilm consumed organic matter, including cholera and typhoid bacteria.
Only one man, physician John Snow, suspected the pathogens to be waterborne, and noted in The Medical Times and Gazette that the company had “in every epidemic very much less cholera in their district.” But without definitive proof, Londoners still blamed the city’s stench.
Snow made his case in the summer of 1854, when more than 500 people in the city’s Soho district died of cholera in a 10-day span. After delving into the victims’ public records, he discovered that nearly all of them lived by a well on Broad Street. Of the minority who lived elsewhere, Snow learned from their surviving family members that those victims had recently drank water delivered from the same source. It turned out that the well adjoined a cesspool, and bacteria had moved from the waste to the water.
Snow presented his findings to community leaders, who agreed to take the well out of service. The move ended the outbreak, and the investigation became one of the earliest studies to support the germ theory of disease.
“That’s really the field of epidemiology,” Salzman says. “The field of public health starts there.”
The Chelsea Waterworks Company’s filter—called the “slow sand filter” for the many hours the water took to pass through the goo—began operating on a large scale through a new, piped water supply at this time, and the technology spread throughout the world.
Near the end of the century, scientists in Louisville, Kentucky, adapted this filter to remove mud from its local supply. Because mud is just earth mixed with water, the scientists developed a scheme to separate out the earth. They stirred the water in a basin and added a metal salt, which caused the particles to collide and connect into larger pieces. The earth settled at the bottom of the basin while the water flowed to the sand, where any remaining pieces could be taken out. The sand didn’t even require a biofilm (it was backwashed to prevent one from forming), so the water moved much faster.
More than a century later, we still use both slow and rapid sand filtration in modern water treatment. In many places, these are supplemented by filtration of the sewage itself, especially where effluent is returned to the river from which the water originated. These processes include screening out debris, detaching solid materials from the water, and breaking down organic matter with microbes.
All this filtration is also regularly combined with another treatment, the final step before water is sent to our homes: disinfection.
Since at least the 1850s, the scientific community has known that chlorine can destroy bacteria. The chemical is abundant in salt brine, but it was difficult to extract on a large scale until the early 20th century, when electrolysis became mainstream and gave treatment plants a means to pry it loose on site.
Chlorine caught on in the U.S. starting in 1908, when a legal battle between Jersey City, New Jersey and a local water supply company ignited a debate in chemistry. The city contended that its new water supply needed filtration, while the company argued just for cheaper chlorination.
The company added chlorine to the water, and the chemical proved to be, according to the judge, “effective and capable” of disinfecting known germs. Ever since then, chlorine has been such an effective disinfectant that the Centers for Disease Control and Prevention considers it one of the most important achievements in public health in the past century. Sometimes it’s combined with or replaced by newer disinfection methods, such as ultraviolet radiation, but the chemical is used almost everywhere in the country.
New Century, New Problems
Despite so much progress, modern drinking water technology has had its flaws. About 6 to 10 million water service lines in the United States are made of lead, a malleable metal that’s easy to shape into pipes but toxic to the human brain and nervous system. The federal government outlawed lead in pipe construction in the 1980s, and additives like orthophosphate prevent it from corroding into the water.
The world witnessed the dire consequences of omitting the compound in 2014, when officials in Flint, Michigan failed to properly treat its new water supply from the Flint River. This disastrous decision caused lead to enter taps at quantities 50 times higher than the threshold set by the Environmental Protection Agency (EPA). The crisis took years to fix, and has fractured residents’ trust in the city’s water.
Like much of America’s infrastructure, crucial arteries of drinking water are breaking down. Many conduits date back at least a century and constantly need repairs. Earlier this year, the American Society of Civil Engineers (ASCE) estimated that a U.S. water main breaks every two minutes, leaking about 6 million gallons of treated water every day.
“Our underground infrastructure is past its design life,” Sedlak says, “and one of the most expensive parts about maintaining a city’s water infrastructure is repairing the pipes as they wear out.”
Repairs will cost billions of dollars, according to the ASCE, and in the long run it may not even be the right solution. There is an unintended consequence to the construction of much of our water infrastructure: when we draw water from one place, we deprive it from another. Rivers, lakes, and aquifers no longer refill at the same rate at which they’re tapped. When the Los Angeles Aqueduct was built, it diverted water away from Owens Lake, drying the landscape and enabling air-polluting dust storms.
Overdrafting conflates with climate change, which is reducing the amount of fresh water that returns to the planet’s surface through snow and rain. A case in point: the Colorado River, a water source for almost 40 million Americans, now receives less snowfall from the Rocky Mountains, and no longer reaches Mexico.
We can address these challenges in many ways, from capturing stormwater for irrigation to using high-efficiency washing machines. But to tackle a global crisis, our drinking water needs to adapt. The world has two practicable solutions:
As fresh water levels continue to decline, we can no longer replicate the aqueducts built for Rome, New York, and Los Angeles. But between potable water reuse and desalination, scientists and engineers have developed some of the first technological solutions to this challenge. And if this history has taught us anything, it’s that a crisis will propel a new wave of innovation—whether it’s a booming population in the Mediterranean, a devastating pandemic, or an increasingly warming (and inhospitable) world.
“Every society in human history has faced essentially the identical problem that we face,” Salzman says. “How do you identify a source of drinking water? How do you make it safe to drink? And how do you get it to the point of consumption so the water stays safe to drink? That was the same challenge 5,000 years ago, the same challenge 5,000 years from now.”