Thirsty Places: Montevideo

The Rambla of Montevideo runs for twenty kilometres along the water, and the water it runs along looks like the sea. It is brown rather than blue, the far shore is over the horizon, the waves break on the rocks below the promenade, and the people who walk it in the evening with their flasks of mate call it the river, because it is one: the Río de la Plata, the estuary of the Paraná and the Uruguay, two hundred kilometres wide at its mouth, which carries the water of a fifth of South America past the city on its way to the Atlantic. Uruguay has, per person, more fresh water than almost any country on Earth. In the winter of 2023 its capital nearly ran out.

This article is about where Montevideo's water comes from and why one reservoir carries most of the country, what three dry years did to it, how the utility kept the taps running by making the water salty, and what the city is building so that it does not happen again.

One river

Montevideo and its region, where about sixty percent of Uruguay's three and a half million people live, drink from the Santa Lucía, a modest river that rises in the low hills of the interior and reaches the estuary just west of the city. The water is taken at a works called Aguas Corrientes, built in the 1870s and still the country's largest, and since the 1980s it has been secured by a single reservoir upstream, Paso Severino, on a tributary, which holds about sixty days of the region's water and is the only large store the system has. The Río de la Plata, which flows past the city a few kilometres away in volumes a thousand times what the city uses, was never used for drinking, because it is brackish: the tide pushes the sea up the estuary, the salt swings with the wind and the season, and the water at Montevideo is on some days fresh and on others a third as salty as the sea. The country had the river for a sea and the Santa Lucía for a tap, and for a century the arrangement held, because it rained.

The Santa Lucía has its own troubles, which the drought made worse. Its basin is dairy and arable country, and the fertiliser and the slurry of the farms reach the river and the reservoir, so that Paso Severino blooms with algae most summers, as the phosphorus article on this site describes, and the works at Aguas Corrientes has had to add carbon and change its chemistry to keep the taste and the toxins out of the tap. In the drought years the river carried the same load in a fraction of the water, and the reservoir, warm and low, bloomed worse. The utility had already begun a programme to protect the basin, with buffer strips along the banks and rules for the dairy farms, when the drought arrived and turned a water quality problem into a water quantity one.

Three dry years

The drought began in 2020 and did not end. La Niña held the rain off the plains of the River Plate for three years running, the cattle died in the fields, the soy harvest halved, and the rivers of the interior fell to their beds. The Santa Lucía fell with them, and through the summer of 2022 to 2023, which is December to March, Paso Severino drained faster than it had in its history. By May 2023 it was below ten percent and falling, the Santa Lucía's own flow was barely enough to cover the intake, and the utility, OSE, was counting the days: in early June the reservoir was under two percent, which is mud, and the city had, on the arithmetic, about ten days of fresh water at normal use.

There was no second source to turn to, and a new one could not be built in ten days. What could be done was to take water from the estuary, which the works could reach through an old channel at the mouth of the Santa Lucía, and mix it into the supply. The estuary water was brackish, with sodium and chloride far above the drinking water standard, and the mix that would stretch the reservoir was over the limit too, so in May and again in June the health ministry raised the limit: sodium from 200 to 440 milligrams per litre, chloride from 250 to 720, with an advisory that the water was safe for most people for a limited period and that pregnant women, infants, people with kidney disease, high blood pressure or heart failure should drink bottled water instead. The TDS article on this site explains what those numbers mean; in the kitchen they meant that the tap water tasted of the sea, that the coffee was strange and the pasta did not need salting, and that the water was, by the country's own standard for the previous forty years, not drinking water.

Two months of salt

The government declared a water emergency for the metropolitan area on 19 June, removed the tax on bottled water, and distributed it free to the poorest households and to schools, and for the next two months the city drank from bottles. The supermarkets ran out within days of the first announcement and rationed what came; the price of the two litre bottle rose anyway; the hospitals, whose water the article on that subject describes, trucked in fresh water for their dialysis units and kitchens; and the restaurants put signs in the window about the water they used. The bottled water companies, which draw from springs and wells in the interior, ran their lines around the clock. The protests that filled the Rambla carried a line that became the summer's slogan, "no es sequía, es saqueo", it is not drought, it is plunder, aimed at the irrigation of the rice and soy fields and at the pulp mills that take water from the Uruguay river, and at a state that had known for twenty years that the capital had one reservoir and had not built the second. The emergency was, in the end, lifted by the weather: heavy rain in August filled Paso Severino in weeks, the estuary water was cut from the mix, and by September the tap was fresh.

What comes next

Two projects came out of the summer, both of which had been on the drawing board for a decade. The first is a second reservoir on the Santa Lucía, at Casupá upstream of Paso Severino, which would roughly double the store and which the previous government had financed and the next one shelved. The second is the one the current government chose: a plant on the Río de la Plata itself, at Arazatí, forty kilometres west of the city, that would take estuary water, treat it, and hold a reserve in a basin on the shore for the days when the salt is high, delivering about two hundred thousand cubic metres a day, which is a large share of the city's use, through a new pipeline. It is called Neptuno, it is built and run by a private consortium, and it is, in effect, a brackish water plant on a sea that is sometimes a river, with the desalination article's questions about energy and cost attached and the argument about private water on top. Both projects will take years. The city that drank salt for two months is relying, until then, on the Santa Lucía and the rain.

What it teaches

Montevideo is the city on this site that nearly ran dry in a country that has no shortage of water, which is the lesson in its purest form: scarcity is a matter of where the water is stored and which pipe reaches it, and a river the size of a sea is no use to a works built on a stream. The state's answer in June 2023 was the one that kept the taps running, which was to change the definition of drinking water for a summer, and it was honest about it. The slogan on the Rambla was right that the drought alone did not do it; a country that had a single reservoir for its capital had made a choice, over decades, not to spend on the second. The rain came in August, the reservoir filled in weeks, and the plant on the estuary will take years. The next dry year is not on a schedule.

Two percent in the reservoir, 440 milligrams of sodium in the tap, and two months in which the capital of a wet country drank from bottles.