Rainwater Harvest: A Solution to Our Water Crisis?

May 30, 2017

by Tamanna Mohapatra   Anyone following the climate change debate is acutely aware of a few facts – the rising temperature of our earth, melting glaciers around the world, the lack of urgency to take action on the part of most world leaders, and last but not the least, the alarming depletion of water resources.  According to the United Nations, “Water scarcity affects more than 40 per cent of the global population and is projected to rise. It is estimated that 783 million people do not have access to clean water and over 1.7 billion people are currently living in river basins where water use exceeds recharge.”   But people who know these facts also know that we can still solve our climate change problems, and that in most cases, it’s not a matter of scarcity but a matter of good management. According to the World Water Council, “there is a water crisis today. But the crisis is not about having too little water to satisfy our needs. It is a crisis of managing water so badly that billions of people – and the environment – suffer badly.” Sustainability advocates know that for each climate change symptom, there is more than one solution. When it comes to solving the problem of water scarcity, one solution is rainwater harvesting (RWH), an ancient concept that has gained quite a bit of popularity recently because of its ease of implementation and its scalability.   Rainwater harvesting involves collecting water from roofs and other surfaces, and directing it to a storage tank for later use.  Rainwater can be used without any processing to flush toilets, wash cars and water your garden.  Using non-potable water for these purposes cuts down on resources needed to process water for consumption.   It sounds simple enough – now how is RWH being applied in practice?   Mexico City: A Work in Progress In 2017, Mexican water technology giant Rotoplas funded a study showing that rainwater harvesting has great potential to source water for domestic users, even in the poorer neighborhoods of Mexico City. This is especially true for a neighborhood with homes not connected to the city’s water network. Mexico City has one of the greatest demands for water of any city in the world – 300 liters per person per day for each of its 9 million residents and many more millions of people who work there. Researchers found that rainwater harvest could supply 60 percent of the average annual percent demand for this population.   Rainwater harvesting can be a boon in a place like Mexico City, where drying aquifers are causing the city to sink into the earth, leading to government rationing and service cuts. While water is lost through old, leaking water pipes, heavy rains often cause flooding.  The storm runoff contaminates the water supply and around 20 percent of the rain ends up in the sewers.   But the future can be bright for Mexico City, and Mexico in general, if rainwater harvesting can prove itself as an economically viable solution. But these solutions require many pieces to fall in place, such as the availability of technology, government pricing water at its true cost, and the presence of local NGOs to promote and teach the application of the technology. Mexico City is lucky to have such an organization.  Over the past eight years, Isla Urbana has been introducing rainwater harvesting benefits to poor communities all around the city.   Scaling Up More and more governments are looking at RWH as a means to supply an ever decreasing natural resource to an ever increasing population.  From an infrastructure perspective, it reduces stormwater runoff from homes and businesses. It is also a very simple technology which can be easily retrofitted to an existing structure or added during new home construction. For the most part, RWH systems are very flexible and can be modular in nature, allowing easy relocation, if and when necessary.   Research shows that rainwater harvesting is indeed a scalable technology. Take the case of India, a country which can get up to 1,000 litres of rainwater during the heavy monsoons. In the southern state of Kerala, the government recently constructed about 87,000 rainwater harvesting pits across residences, schools and offices. They expect these pits to last up to five years, with minimum maintenance.   In Singapore, a rainwater harvesting system was implemented on the roof of a 15-story building. The collected roof water was diverted to two rainwater tanks and used in the building’s toilets with no processing or treatment. If treated, the water could have been used for other purposes as well. This example is particularly relevant for New York City.  Keeping in mind the number of high rises in Manhattan, it’s completely feasible to use rainwater systems in New York apartment buildings.   Show Me the Money: What’s the ROI? Although some critics say that RWH is not cost-effective in the short-term, there are a number of things to consider when determining the return on investment.   Droughts caused by climate change, combined with increased demand for water due to population growth, have severely depleted aquifers. As a result, water rates are on the rise. Another factor to consider is cost of installation versus savings from usage. In locations where no municipal water system is available, and where drilling wells can be very expensive, harvesting rainwater is a smart economic and environmental choice. Another decision factor is indoor versus outdoor use of the collected water. Collecting rainwater for outdoor use, such as watering a lawn, requires no complicated filtration systems or plumbing. However, to convert the collected rainwater to drinking water would require a proper filtration system and therefore, have a relatively longer ROI.   A cost benefit analysis to calculate ROI needs to consider upfront costs to install the system compared to estimated annual savings: Payback Period = Upfront Installation Cost/ Estimated Annual Savings.   It goes without saying that the payback period will vary based on a number of factors, including the amount of local rainfall, the size of the implementation, financing, rebate incentives, usage, local water rates, etc.   Water on the Homefront The water needs of NYC are not insignificant. According to NYC Open Data, the city used 1,002 million gallons of water per day in 2016.  Per capita, that equated to 117 gallons per person per day.  And Superstorm Sandy proved that New York is not immune to weather vagaries. It is true that we need an arsenal of solutions to fight any future extreme weather fluctuations, but rainwater harvesting can be adapted as one of those solutions, solving two problems at once – storing water for future use and helping to reduce stormwater runoff.   Believe it or not, RWH is already a tested and applied technology in New York City. One great example is at the Department of Sanitation. A 1.5 acre green roof reduces heat-island effect, and both captures and filters rainwater, which is then used for toilets and washing sanitation trucks. Combined with low-flow fixtures, the system reduced water usage by 77%.   Many local NGOs, such as GrowNYC and Water Resource Group, have been educating New Yorkers on how to start a rainwater harvest project.  GreenThumb, a community gardening program supported by New York City Parks and Recreation, lists about 20 gardens all across the city that already have a rainwater harvest system installed.  And NYC’s Department of Environmental Protection recently started a Rain Barrel Giveaway Program as part of their Green Infrastructure Plan, a $2.4 billion investment in green infrastructure projects, including rain barrels. The program aims to capture stormwater before it enters the sewer system, with a goal to reduce combined sewer overflows into local waterways by 2030.  The 60-gallon barrels connect to a property owner’s downspout, collecting water from the roof for use in outdoor chores.  Go get yours and be part of the solution!