Let it Rain: Harvesting Rainwater in Mexico City

Mexico City, a metropolitan area with a population of over 21 million people, is facing serious water issues. So much so that 8 million residents suffer from inadequate water supply, sometimes going weeks or months without a drop of water coming from their taps.

The city infrastructure is struggling with the fact that 70% of the water supply coming from the over-extracted aquifer of the Valley of Mexico, which is actually causing the city to sink about 1 meter every 10 years.

Meanwhile, for several months of the year, there are heavy rains that cause flooding throughout the city, which is exacerbated by the continued sinking of the city.


Clearly the people of Mexico City need solutions, and Isla Urbana is doing something about it. The organization is implementing rainwater harvesting (RWH) systems throughout the city as well as in surrounding rural areas.

By capturing rain that is falling on their roofs, a home can supply 50% of its water needs, and if implemented on a large scale, Isla Urbana estimates that RWH could provide 30% of Mexico City’s entire water supply, providing much needed relief for an overtaxed infrastructure that uses tremendous energy to pump water over great distances.


How the Rainwater Harvesting Systems Work
Simply put, rainwater harvesting systems harvest rain from roofs and put that water to use in homes. There are a variety of types of installations and levels of integration, but essentially, rain falls on the roof, is properly funneled to a collection point where the initial debris from the roof is filtered off (first flush), then piped into a cistern (holding tank), which is then pumped into the house for use, as illustrated below:


Many homes still use 5 gallon jugs (garrafóns) for drinking water, thus saving on the expense of a filtering system. Isla Urbana does also install filters for drinking water as well as partnering with a company to provide ceramic filters.

This video shows how the first flush system works, and Isla Urbana has a variety of videos on their YouTube page explaining how things work

Isla Urbana has been creating a lot of impact since its inception in 2009, and here are some stats to date:


  • Number of Systems Installed: 1,315
  • Beneficiaries: 9,521
  • Number of Liters Captured: 137,079,718
  • Water Trucks Saved: 10,000

Implementing the Systems
Having a logistical solution to getting people water is only the first step. Spreading the word, building trust and connection, and getting buy-in involves a lot of hard work. Renata Fenton, co-founder of Isla Urbana told me that the most effective contacts have come from existing organizations already working in areas of need.

Having existing relationships and trust is a huge head-start, but making sure the systems are set up and working properly is extremely important. Even though RWH is a viable, economical, sustainable solution for many families, there is skepticism at first, and if the installed system doesn’t function properly, the view is that RWH won’t work, not that the system just had a faulty pipe.

As Renata told me,

If the systems don’t function well for the beneficiaries it is not that our system doesn’t work it is that rainwater harvesting doesn’t, that is very dangerous in a community that is working with the technology for the first time.

Overall, things are going quite well. The systems are low-cost, are installed in about one day, are easy to maintain, and provide clean water for all household uses.

Paying for Water
As many other social projects have proven, when beneficiaries pay for something, there is more of a buy-in and sense of ownership. While the majority of the system cost is covered by private funding, Isla Urbana has different ways of structuring the cost to the families.

We have found that a cost to the family, whatever percentage it may be, will increase the probabilities of that family adopting the system effectively.

In marginalized, water-stressed communities, Isla Urbana charges families a portion of the actual cost, and in cases where the house already has a pump and cistern, the family simply pays the plumbers for the installation $1,000 pesos or about $75USD. The organization is in the early stages of working with Kiva to offer loans as well.

In other areas the government funds the systems and in those cases the families are not allowed to be charged a fee. In order to get buy-in in those situations, the families are asked to help prepare for the installation with jobs such as flattening the terrain for their cistern or digging trenches for their grey water filters, etc.

For the general public that has the resources, Isla Urbana provides kits that output varying levels of water quality and quantity that are paid for in full.

Construction Issues
Renata told me that one of the main construction issues that they run into is the way roofs have been built to divert water in many different directions, including pipes that run through walls. Isla Urbana has a few different options for addressing this issue and they have gotten more efficient with it over time, including using only part of the roof for RWH.

Building a Community and Providing Education
Isla Urbana does much more than simply install RWH systems to provide water.

When a system is installed, a training session is held with the family, and instruction manuals and a training video are provided. Then, right before the rainy season, representatives of Isla Urbana visit the families to they have everything clear and have replaced their cartridges and are ready to capture rain.

In addition, all materials are bought locally at neighborhood hardware stores, they train local plumbers, they educate people in the communities they serve, and they partner with other organizations on various projects.

By training local plumbers, there is a pool of local knowledge to deal with any problems that may arise. Buying the materials locally also ensures that the communities have the resources necessary to maintain their systems.

To help build awareness and education, Isla Urbana offers courses on rainwater harvesting that vary from an introductory course that lasts a few hours to a two-day intensive course to teach people how to construct a full-scale system, and hosts community events to promote participation in the improvement of the community where we are currently living and working in Mexico City.

Community Events
Isla Urbana also works on community building as well as working with children. One of the ways they do this is by partnering with with another organization called Concentrarte to provide after-school activities for the children in the community and on raising awareness of environmental issues as well as awareness of rainwater, the cycles, harvesting rain, how the systems work, the essentials of bathing and brushing teeth, using art to help educate.


Funding Challenges
As with many non-profit organizations, finding consistent, long-term funding sources remains a challenge. In the meantime, Isla Urbana is working to address serious water issues. Given the proven success of the systems and the connections to communities, the organization would make a great potential partner for any social enterprises focused on solving water issues. Of course, if you’d like to support them now, they will be appreciative to receive financial or volunteer support.

Setting up a Model for Replication
The Mexico City area has a couple factors that are helping with RWH adoption. First, there is a severe water crisis making people open to new ideas, and logistically most homes (even in marginalized areas) already have cisterns and pumps, which accounts for 80% of the cost of the system. In addition, the area receives a lot of rain, which makes RWH a very viable option.

By gaining adoption and seeing successful results, Isla Urbana strives to serve as a model of the implementation process to be replicated throughout the city and the world.

For more information on Isla Urbana, check out www.islaurbana.org, www.islaurbana.mx and connect with Isla Urbana on Facebook, YouTube, and Twitter.

If you have examples of other large-scale rainwater harvesting efforts, other methods of solving water access, or ideas on how to help, please leave them in the comments.

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