Save it for a rainy day: Roof-Harvesting Rainwater in the Sonoran Desert
Today, water shortages affect 1 out of 9 people. To put this in perspective, imagine a room with 9 people in it, 8 of those people may grab a cup full of water from a pitcher in the room but 1 person must walk thirty minutes for the same cup of water. Water shortages are not limited to dry environments, like Tucson, places with a stable water supply can, unfortunately, lack the infrastructure to provide access to safe drinking water. Imagine you were that unlucky person who had to walk for a drink of water. However, there are places where you do not have to walk thirty minutes because there is abundant groundwater but the infrastructure to supply is yet to be constructed. You may be thinking, drilling wells, pumping the groundwater, treating it to safe drinking standards and designing the delivery system will be rather costly. It is. But are there economical alternatives that can provide safe drinking water to rural communities around the globe? Luckily for us, there are, and one we have been practicing for over 4,000 years: rainwater harvesting.
The capturing and storing of rainwater goes back thousands of years to when we first started to farm the land and needed to find new ways of irrigating crops. In dry climates, collecting the rainfall often meant the difference between life and death for communities. With urbanization, the need to conserve water fell away in the last thousand years. Today, global water shortages return us to this old-fashioned, low technology and critical part of sustainable living. A common technique that has been used for hundreds of years in India, Brazil, and China is to build water harvesting systems on top of the roofs of houses. It’s a simple technology that has spread across the world, particularly to countries such as Honduras, Dominican Republic, Paraguay, and the United States. Together we can combat water shortages by conserving, protecting and maximizing our existing water supply, roof-harvested rainwater can be reused for irrigation and garden, laundry and toilet flushing!
What is the first thought that comes to mind as you hear the rainfall? Is it an image of children jumping from puddle to puddle? Or perhaps you think of petrichor: that pleasant smell that frequently accompanies the first rain after a long period of warm, dry weather. These thoughts also rush to my mind as I attempt to grasp that idle umbrella that has been hiding quite successfully beneath a heap of cardigans overflowing the coat rack. With the umbrella on hand, I step into the rain. As I stand motionless under the umbrella I see the raindrops fall vertically, yet I remain dry and I think of rainwater quality. As an engineer, I wonder how raindrops form. As a chemist, I ponder what chemicals exist peacefully almost unnoticeable within a raindrop? Water is an interconnected system. What is poured on the ground today can end up in our drinking water years later. If we plan to use roof-harvested rainwater for food production and possibly drinking, perhaps an important query is what is the quality of a raindrop? Sir Isaac Newton once said, “What we know is a drop, what we do not know is an ocean.”
Visualize a raindrop as it falls on your roof and travels down to a collection reservoir. At this moment, you try to remember the last time you cleaned it. Suddenly, you recall the three buckets of sealants you applied for protection last summer and the eight lines of ingredients you did not recognize. Envision that electric blue plastic reservoir a used for capturing and storing that has been sitting outside all summer in the heat. What is that blue plastic reservoir even made out of? Could some of the materials we use to harvest rainwater dissolve into that water?
Currently, national rainwater quality standards for both potable and non-potable domestic usages are yet to be determined. My dissertation research explores the presence or absence of chemical pollutants in rainwater. My goal is to identify and quantify chemical pollutants in rooftop harvested rainwater samples, our overall goal is to generate a dataset that will inform guidelines and recommendations for safe, harvested rainwater use. My desire to spotlight this issue extends even to children, the smallest victims of water pollution. With the help of CLIMAS, I will be producing a book on the topics of rain formation, water conservation, pollution and uses which children would illustrate and for which I will provide age-appropriate explanations.