Water-Wise: Building a Rainwater Collection System *

Abstract

We are all familiar with the nursery rhyme, "Rain, rain, go away, come again some other day…", or the song "Singin' in the Rain." Numerous songs and stories describe our feelings about rain. Why so many? Because we humans understand how important rain is to our well-being. Rainfall, as part of the water cycle, brings water back to Earth that had previously evaporated or transpired from the surface. When water vapor in the atmosphere condenses into clouds and falls back to Earth as rain, it lands on oceans, lakes, and the ground, where it soaks in and recharges the groundwater supply. Groundwater serves humans, animals, plants, and microorganisms alike.

For the people who live in the Thar Desert of India and in the western part of the semi-arid Sahel and Sudan belt that crosses Africa, the rain that falls during the monsoon season is especially important because it is often the only source of water. The monsoon occurs in certain parts of the world when seasonal winds reverse, bringing in dramatic weather changes. Summer monsoons usher in heavy rains while winter monsoons can result in drought. In these parts of the world, collecting rainwater is an important task, one that provides both drinking and cooking water. For hundreds of years, the people living here have developed different methods of collecting water. Watch this video of a talk given by Anupam Mishra, a founding member of the Gandhi Peace Foundation. He travels across India studying and sharing rainwater harvesting techniques.

Watch this video in which Anupam Mishra gives a TED talk on rainwater collection techniques practiced by Indian desert dwellers. (Video by TED.com)

You may think that collecting rainwater is an ancient art practiced only by people living in arid and developing regions of the world, but this is not true. People in urban areas collect rainwater, too, although it is a non-potable water source. This means that it is not safe to drink. However, it can still be used to water landscaping and to flush toilets. While this rainwater may contain contaminants, such as chemicals, molds, dirt, bird feces, and leaves, consumers can take measures to clean and disinfect the water, with ozone or chlorine, and then they can drink it. Using rainwater is a way to reduce dependence on the municipal water utility, alleviate runoff, and live a sustainable, "green" life.

One common way of collecting rainwater is to divert the rainwater from a rooftop. Simply, the rain flows down the roof, into a gutter, and then into a holding tank. Holding tanks can be made from clay, cement, wood, or plastic. Figure 1 shows a concrete rainwater tank in Kerala, India. Notice the gray pipe that connects the tank to the roof.

Figure 1. A 35,000-liter rainwater harvesting tank in the state of Kerala, India. (Wikipedia, 2011)

The tank is covered to prevent mosquitoes from breeding in it, and to keep leaf litter and other large foreign objects from falling in. Toward the bottom and on the side of the tank is a spigot, to which a hose can be connected. Some complicated systems have first-flush valves (to discard the water from the first rainfall, which likely has roof debris and particles in it), filters that remove particulates and harmful substances, and disinfection systems that kill bacteria. Disinfection occurs as the last step, just before ingestion of the water.

For your science project, try designing and building a rainwater collection system for non-potable water use. Remember that the collected water is not for drinking. The Engineering Design Process guide can help you organize your thoughts on how to get started. In addition, there are several sources online from which you can get ideas and plans on how to build a collection system. The references in the bibliography are a good starting place, but make sure to do your own research. You will have to take several issues into account, the most important being that the collection of rainfall in some states in the United States is subject to water-rights limitations. Look into your state's water laws prior to starting this project. Another issue to consider is the kind of roof you will be collecting the water from. What kinds of roofs add contamination to the water? Is one type of roof better for collecting rainwater than another? What is the average rainfall in the area in which you live? How much water can you harvest in a month? In six months? How much money can your household save? Is collecting rainwater useful for your household?

Credits

Michelle Maranowski, PhD, Science Buddies

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Bibliography

• Pushard, D. (2005). Rainwater harvesting: Frequently asked questions. HarvestH2O.com. Retrieved December 20, 2011, from http://www.harvesth2o.com/faq.shtml#1.
• TED Conferences, LLC. (2009, December). Anupam Mishra: The ancient ingenuity of water harvesting. Retrieved December 20, 2011, from www.ted.com/talks/anupam_mishra_the_ancient_ingenuity_of_water_harvesting.html
• NSF. (2004). Rainwater collection. Retrieved December 20, 2011, from www.nsf.org/consumer/rainwater_collection/index.asp?program=WaterTre
• Moseman, A. (2009, December 18). Who owns the rain? Hint: it's not always homeowners. Popular Mechanics. Retrieved December 20, 2011, from www.popularmechanics.com/science/environment/water/4314447

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