Avoiding A Fresh Water Crisis

Day Zero is a scary idea. Defined as the day when a major metropolitan area runs out of water because of drought, the term became popularized in 2018 when Cape Town, South Africa nearly ran out of — and began having to ration — water.

The original Day Zero crisis, though, happened halfway around the world and several years earlier: in São Paulo, Brazil, in 2014 and 2015.

With a metropolitan population of more than 20 million people, the coastal city draws about one quarter of its municipal water resources from a nearby watershed called the Cantareira Water Supply System. But when the 2014 drought — the worst in nearly 100 years — reduced the city’s water coffers to under 5 percent capacity and dried up a significant part of the reservoirs in the Cantareira system, the crisis sparked a second realization: for years, the areas around the watershed had been steadily degraded.

Due to a combination of land misuse, agricultural pollution and climatic changes, the formerly verdant watershed had been deprived of much of its original forest cover, which protected the water supply and kept the reservoirs healthy. By 2013, 70 percent of the forests in the Cantareira region had been destroyed, replaced instead with degraded pastures.

The Cantareira System needed a revamp.


The Cantareira System, developed in the 1970s, operates in a delicate balance. Water originates from a series of five reservoirs and filters through a complex system of underground tunnels and an elevation plant before reaching the Guarau Water Treatment Station in the outskirts of Sao Paulo.

These initial reservoirs play a critical role: capturing the large majority (87 percent) of sediments ― small particles that pollute drinking water and cause damage to infrastructure — and preventing them from filtering into the water supply.

When reservoirs like the Jaguari, one of the five that feeds the Cantareira system, are surrounded by forests, trees naturally prevent erosion of sediments into the water source. As forests are replaced with pastures, however, erosion accelerates.

Local landowners — who are typically low-income, making under $200 per month, and rely on traditional agriculture to get by — play a key role in protecting these ecosystems, but often lack the training and resources to do so in a sustainable fashion.


The 2014-2015 drought was an eye-opener for the Brazilian government.

Since the drought ended, São Paulo’s water company, Sabesp, has begun to invest in watershed management practices and training for local farmers with a focus on natural infrastructure: “green” as opposed to “grey” solutions. Instead of building more underground tunnels to filter water from additional reservoirs, the company has looked to improve the existing water resources through forest restoration projects and silviculture.

Riparian forests — or forested wetlands — play a key ecosystem role, reducing erosion by more than one-third and helping to increase biodiversity, while also improving the resilience and longevity of watersheds.

But restoring these forests in places like southeastern Brazil isn’t just an environmental choice. It’s also an economic one. According to a report from the World Resources Institute, investing $37 million in ecosystem restoration projects would save the Brazilian state nearly $70 million in costs due to erosion and negative health consequences due to unclean water over the next 30 years.


For the Caterpillar Foundation, restoring local ecosystems and investing in protection of the natural and vital infrastructure is one of the key ways that we can help communities grow stronger, more resilient and more sustainable.

Through our work with partners in Brazil, we know that addressing the water supply and infrastructure challenges is critical to the future health and prosperity of their communities. Our approach to help addressing this issue in Sao Paulo was to focus on the Cantareira System, which was once able to provide water to half of Sao Paulo’s population and it now only services one-quarter.

With continued population growth, and extreme weather events increase over the coming years due to climate change, we knew that the resiliency of the system will be even further tested. We joined a number of organizations that stepped up to address these challenges, notably by providing training to local landowners on the frontlines of the water scarcity fight.

In particular, we partnered with Semeando Agua (or “Sowing Water”), an initiative run by the Instituto de Pesquisas Ecológicas (IPÊ), to implement sustainable production practice techniques using native species, restore native forests in priority areas, and apply low-cost forest restoration models in the Cantareira System.

The IPÊ also runs a number of educational programs in public schools — training the next generation of students in resilient watershed management techniques.

But we know there is a lot more work to do to ensure long-term resilience in this area. According to IPÊ’s estimates, producers will need to restore about 20,000 hectares of natural forest in the coming years to avoid further degradation to the watershed ― the equivalent of planting about 35 million trees.

So as environmental and human factors threaten to produce another Day Zero, we at the Foundation firmly believe that investing in natural infrastructure can be one of the key ways to protecting future water supplies and building thriving communities for the years to come.