Publicada el 22 de Marzo de 2021
In 2018, Cape Town was only months away from what they called Day Zero. The words had an apocalyptical sound when they were spoken for the first time. For the people of Cape Town, Day Zero would mean huge changes because on Day Zero, they would run out of water.
Since then, the original date has been pushed back. Cape Town teetered on the brink and the population pulled together to avert this catastrophe. But Day Zero hasn’t disappeared, it’s just been delayed… again.
As the world heats up, Cape Town is just the first on a list of big cities on the brink of seeing their reservoirs run dry. And the problem doesn’t just lie in South Africa. Cities like Sao Paulo, Mexico City and even the state of Texas have been slowly walking the path towards their own potentially catastrophic Day Zero. So, have lessons been learned from the Cape Town crisis, or are other cities walking blindly into the same mistake?
Houston, we have a problem
For the last 150 years Houston has been relying on groundwater for pretty much all of its water needs; for drinking, agriculture and industry. And after a century and a half, it’s finally starting to show through something called subsidence. In other words, the city is sinking.
Because so much groundwater has been taken out from beneath Houston, the city has sunk about 10-12 feet in the last 100 years. That’s about the height of two people. Mexico City, probably the most famous subsiding city, has it even worse, as today many of its buildings crack and tilt due to empty pockets of earth where groundwater has been drained.
Because Texas is so reliant on groundwater, the government has had to step in to avoid a Mexico City style subsidence problem. Their mandate was a move away from groundwater and shfit towards surface water sources. And with 1000 new residents arriving in Texas each day, this seems like a smart move, especially with northern parts of the state sinking at a rate of 1-2 inches per year.
The government mandate has seen cities such as Houston, San Antonio and Dallas/Fort Worth spend billions over the last decade to diversify their water sources. Surface water is definitely more expensive to treat than ground water (or even the semi-salty brackish water), but billions invested in diversifying the system now could save a lot more in the future.
So what does a diversified water system look like? Well, there’s water from lakes, water from reservoirs, groundwater of course, and finally, the socially stigmatized yet pretty amazing wastewater.
The glass is definitely half full
When you realize that the groundwater in Houston was being used for everything, you begin to see the complexity of the situation. Because to say it was used for everything means the city was using an ideal source of drinking water for industry and agriculture too. This is often the norm across the world, just not very sustainable when we think of our exponentially growing water needs in the future.
The problem with industrial and agricultural water needs is that they simply use a lot of water. The other problem is that a city needs a certain amount of industry for it to be successful. A balance needs to be struck, because the city needs to be able to supply that industry with a reliable source of water. Enter recycled wastewater.
Wastewater is, in effect, sewage. But as technology advances in the treatment process, our view of it as a water source needs to advance too. States like Texas and California are already using treated wastewater to water crops with incredible success. Golf courses that were once watered with groundwater are now being watered with wastewater. Treated wastewater is even being fed into reservoirs where drinking water is later extracted, something totally legal and totally safe. This type of re-use is called indirect potable reuse, or IPR.
Wastewater treatment has advanced so much that it’s now possible to run a pipe from the wastewater plant directly to your tap, and safely drink the water that comes from that tap. This is called direct potable reuse (DPR) and is expensive to do, but still a viable, if not frequently used, option.
Understanding how we can reuse wastewater is one of the keys for any state to avoid a Cape Town style Day Zero, and our social attitudes towards it will have to change to begin to use this reliable water source.
Resilience is key
Reusing wastewater and moving to surface water are two of the steps Houston and much of Texas has taken to avoid running out of water. Because Houston sits at sea level, water naturally finds its way towards the city. Their strategy therefore focuses on these two options to reduce groundwater usage.
Other cities across the world can use other methods, including desalination of seawater, something that Houston has the potential to do thanks to its proximity to the Gulf of Mexico. Having all these strategies in place is something called water resilience; basically a reliable water supply that can adapt to changes.
And these changes may come in the form of extreme weather. Within the eight years Texas has seen droughts, hurricanes, flooding and snow. And this extreme weather is part of a wider pattern of climate instability that makes something like water resilience even more important.
Each city will have its own challenges and solutions as it approaches its own Day Zero, but as we become more aware of water usage and where we source that water, we can begin to move away from the habits leading us towards those problems.
Coffee & Knowledge Webinar
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