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Public Radio's Environmental News Magazine (follow us on Google News)

Water Permeable Concrete

Air Date: Week of

Mexico City gets almost 30 inches of rain each year, but most of it runs out to the ocean through extensive drainage systems. During the summer rains, the streets flood and the aquifers are not refilling fast enough to keep the water supply at a constant level. A group of entrepreneurs believe they have a solution to the city’s water problems with a material called “Ecocreto.” Conrad Fox reports.


CURWOOD: Like many cities, Mexico City is strapped for water, and for cash. Water treatment facilities and new supply pipes are badly needed but they’d bust the municipal budget. Now some local inventors believe they have found a surprisingly simple and economic solution to the city’s water woes. And Conrad Fox has our story.


FOX: You wouldn't think the twenty million residents of Mexico City would have to worry about their water supply; they get more than 27 inches of rain every year. But most of that rain never makes it to a tap. Instead, one of the most extensive drainage systems in the world channels it straight out of the city and to the sea.


VOICEOVER: Mexico City gets very short, very intense rains during the summer. We've got to be very efficient about draining the water. And if we don’t get rid of it quickly, not even the Lord our Father could prevent this city from flooding.

FOX: That's Juan Carlos Guasch, technical director of Mexico City’s water system. Flooding is a serious problem in many parts of the city, but keeping streets dry is only half the challenge Guasch’s department faces. The other half is making sure residents still have enough to drink. And at the moment, he says, he's fighting a losing battle.


VOICEOVER: Seventy percent of our water comes from about 450 wells in the city. Some rain does recharge the aquifer but not fast enough. In the south of the city the water table is dropping about a meter a year. That’s not good. In fact, it's extremely bad.

FOX: No one knows for sure just how much water is left in the Mexico City aquifer, although most think a crisis is not far off. But what worries Guasch is that as the aquifer depletes, concentrations of manganese and other dangerous elements make the drinking water almost unusable. And that’s not the only consequence of a sinking water table.


FOX: On a busy sidewalk in the center of Mexico City, Jesus Esteva, a consulting engineer for the city works department, points out the crumbling pavement at the base of an old art deco building. Part of the sidewalk has heaved upwards and passersby are forced to step around the rumble. The problem, says Esteva, is related to what lies below the concrete of Mexico City.


VOICEOVER: It's built over jello. What was once a lake. The ground is very soft clay and water. Most of Mexico City's water comes from the same ground, and as it is pumped out, the ground dries out and sinks. In places you can have sinking up to a meter.

FOX: The problem dates back to the early 17th century when the Spanish drained Lake Texcoco, which covered much of the Valley of Mexico, to build their new capital soon after the conquest of the Aztec Empire. The valley has no natural drainage and flooding was a serious problem, even back then. To handle it, the Spanish built a series of large drainage canals. They worked for a time but soil has since subsided, and the canals now run uphill. And moving soil also means broken pipes. The city loses an estimated 35 percent of its water to leaks, a nightmare for residents like Francisco Gasca.


VOICEOVER: There never used to be a lack of water. I put it down to leaks in the streets. You can often see water bubbling up over the sidewalk. You spend 8 or 10 hours without water in the bathroom, it’s horrible.

FOX: But a group of Mexican entrepreneurs believes they have discovered a solution to the problem. And it happened by accident. One day, in 1996, architect Nestor de Buen and a friend dropped by the lab of chemist Jaime Grau to examine new materials that Grau was developing--mostly paints and paving tiles. They noticed a small paving stone in the corner.

NESTOR: When German asking why he didn't want to show that special piece, he said, “it doesn't work because water goes through it.” So I told him “Jaime, you’re kidding, that's impossible.” So he opened the sink, put the piece under the water and I felt like, you know, like my soul was going everywhere around the world. I told him, “Jaime you just discovered something that everyone around the world is looking for.”

FOX: Grau had hit upon a pervious, water-permeable concrete. It's similar to normal concrete, but has no sand. Instead, a special additive holds the gravel together in a strong but porous block, which some have likened to a big rice krispy square. De Buen convinced Grau to patent the product, and together they began selling it to the Mexican and U.S. construction industry under the name Ecocreto. Ten years on, the name is hardly a household word, but its makers are convinced it could be the saviour of places like Mexico City.


FOX: Ecocreto can be used for roads, parking lots and other surface coverings, just like concrete or asphalt. But unlike traditional paving methods, water runs straight through Ecocreto and back into the ground.


NESTOR: If, if this was rain, it would be more than a year's worth of rain, in this small area.

FOX: Nestor de Buen pours a bucket of water on a parking lot made of Ecocreto. The water disappears instantly, leaving behind just a small wet stain.

NESTOR: In most cities around the world, we take the water from the aquifers but we don’t get it back. And in most places, when cities are built, what we are doing is putting impervious surfaces above the ground so that water is not going to get back when it drains. One of the authorities, when we started this project, told us that if we could give the aquifers one third of their rain water back we would solve the problem pretty fast.

FOX: Others have already recognized Ecocreto's potential for alleviating the water crisis in Mexico City. The product has won several environmental prizes, including one from the World Resources Institute. Some Mexico City officials have promoted its environmental benefits but although it has been used for some public roads and private constructions, its use hasn't been widespread. In most cases, the city has preferred the cheaper alternative - - at least in the short run -- of laying traditional concrete or asphalt for new roads. And it's far from ripping up old ones to lay down Ecocreto. Juan Carlos Guasch says fixing the leaky water supply system already sets the city back 20 million U.S. dollars a year, but it’s not only the cost that concerns him.


VOICEOVER: We think it’s a good product and we’ve recommended local authorities use it. But it’s mostly useful in the south, where the city is growing. Here in the center it doesn’t make any sense because the soil is impermeable.

FOX: According to Ecocreto developers, that problem can be overcome by drilling holes beneath the pavement to allow water to permeate to the aquifer, but that substantially raises the product's cost. Nestor de Buen believes that any solution to Mexico City’s water problems is going to be costly and he’s disappointed that the city isn’t using the product on a larger scale.

Meanwhile, his company is finding new uses for the product. Currently, they're installing it in golf courses under sand traps. And they've partnered with MBA students from Georgetown University to seek new markets in the U.S. But for de Buen, the inspiration remains his thirsty city.

NESTOR: In Mexico, the worst problems are not politicians, which are rather bad most of them. Not the thieves and the kidnappers. The worst problem this country has is the lack of water.

FOX: De Buen knows Ecocreto won’t solve Mexico City’s water problems single-handedly but he believes it’s, at least, a partial solution for the water-strapped city. For Living on Earth, I'm Conrad Fox in Mexico City.

A Living on Earth Exclusive:
Professor Bruce Ferguson, Director of School of Environmental Design at the University of Georgia, Athens, talks with Steve Curwood and porous pavement.
- Advances in Porous Pavement
- Bruce Ferguson, School of Environmental Design





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