The most devastating threat to humanity in the 21st century is the lack of safe drinking water. In 2015, 663 million people globally were denied this elementary right, which imperils health, livelihood, and socio-economic development. Nearly 50 percent of the world’s population will be living in areas of high water stress by 2030.1 Clearly, rapid population acceleration will impose new challenges on water supply and security in the coming decades.
Water scarcity is propelled by two factors: 1) surging population growth in the developing world; and, 2) water depletion and/or contamination caused by global warming and rampant unchecked pollution. Diseases caused by contaminated water and unhealthy sanitation practices are a significant global health burden. Inadequate drinking water, sanitation, and hygiene are estimated to cause 842,000 diarrheal-disease deaths per year.2 According to researchers at the Massachusetts Institute of Technology, five billion people comprising 52 percent of global projected population of 9.7 billion by 2050 will live under conditions of severe water stress, and most of these inhabitants will be living in India, Africa, and the Middle East, areas already burdened by chronic water shortages.3
The linkage between water scarcity and human suffering is sobering: of the 663 million people without clean water, 48 percent live in sub-Saharan Africa. Approximately one in nine people worldwide do not have access to safe and clean drinking water.4 Moreover, 143 million school days are lost each year due to water-related diseases.5 Over half of the world’s hospital beds are occupied with people suffering from illnesses linked with contaminated water, and more people die as a result of polluted water than are killed by all forms of violence, including wars.6
According to U.N. Water, “the most prevalent water quality problem is eutrophication, a result of high-nutrient loads (mainly phosphorus and nitrogen), which substantially impairs beneficial uses of water. Major nutrient sources include agricultural runoff, domestic sewage (also a source of microbial pollution), industrial effluents, and atmospheric inputs from fossil fuel burning and bush fires. Every day, two million tons of sewage and other effluents drain into the world’s waters. The most significant sources of water pollution are lack of adequate treatment of human wastes and inadequately managed and treated industrial and agricultural wastes.”7
The combined effects of population pressure, pollution, and climate change impacts such as drought are contributing to this precarious ecological and health crisis.6 Women, children, and the elderly in the developing world are the worst impacted. One solution that can be particularly cost effective is rainwater harvesting. One recent study noted that, “Rainwater harvesting would be one of the most conceivable and viable solutions to release the pressure on the groundwater table as the system utilizes natural rainwater without affecting groundwater sources.”8
Collecting rainwater is an ancient, effective, and eco-friendly technique that has been utilized for over 3,500 years. It has recorded use in early Greek, Chinese, Roman, and Arab civilizations. It is utilized to provide water for drinking as well as irrigation. Its application is particularly suitable to developing countries where technology and capital can be limited. The harvesting of rainwater is a simple process that involves the collection of water from the various surfaces upon which rainwater falls. Water can be collected from building rooftops, including houses and simple dwellings, and stored in rainwater tanks. The basic essentials include eaves or gutters, down pipes, rainwater drains, filters, and disinfectants. Eaves or rudimentary funnels can collect the water and provide a run-off tube that flows into barrels or storage tanks. The issue of sediment on the roof area or bacteria in the water can be solved by the use of filters and disinfectants.
Basic filtration systems can utilize screen filters, paper filters, and carbon or charcoal filters. A reliable and safe system will depend upon more than one filter device. Often, a 50-micron size filter or equivalent screen is utilized to remove larger particles such as dirt. This would normally be followed by the use of additional 20- and 10-level micron filters, then smaller filters at the 10 and lower micron levels such that particles are progressively screened out. Disinfection of the water source is an important step in rainwater harvesting to eliminate pathogens and unsafe microorganisms. Typical disinfection methods include chlorine, ozonation, ultraviolet (UV) light, and membrane filtration.
A report by Sustainable Sanitation and Water Management, an NGO working towards rural water solutions, observed that rainwater harvesting “is a simple low-cost technique that requires minimum specific expertise or knowledge and offers many benefits. For drinking water purposes in rural areas, the most common technique is small-scale rooftop rainwater harvesting: rainwater is collected on the roof and transported with gutters to a storage reservoir, where it provides water at the point of consumption.”9
“Water run-off from a roof can be directed with little more than a split pipe or piece of bamboo into an old oil drum (provided that it is clean) placed near the roof. The water storage tank or reservoir usually represents the biggest capital investment element of small-scale rooftop urban rainwater harvesting system and therefore requires careful design to provide optimal storage capacity while keeping the cost as low as possible. Installing a water harvesting system at household level can cost anywhere from USD$100 up to $1,000.”10
The fact that rainwater harvesting can be deployed on a small scale and in areas cut off from piped water supply means it offers strong benefits to marginalized and poor communities and is an effective guard against water scarcity and drought. Cisterns are the most popular rainwater harvesting storage technology. In this system, runoff rainwater is diverted from the rooftops of houses via gutters (made of bamboo, plastic, or metal) and stored in a closed tank or jar with a capacity of 5–50m3. In Brazil’s semi-arid region, a rooftop area of 40m2 can capture and store 16,000 liters of clean water for a single household.11 Perhaps most simply, rainwater harvesting means women, who do the bulk of water gathering in arid areas, no longer have to spend hours walking to wells each day, exposing them to danger and exhausting labor.
Let’s take the example of India, the second most populous country in the world and burdened by significant poverty and income inequity. According to World Bank data, in 2010, there were 259.5 million Indians living on USD$1.90 per day.12 The country houses 16 percent of the global population, yet only four percent of global water resources. By 2050, the population is expected to reach 1.6 billion people, surpassing China.13 Water stress is clearly evident in India, and as population surges, this situation will be exacerbated to the point of water scarcity in many parts of the country. In 2011, India had a per capita water availability of 1,545m3, a significant decrease from 5,177m3 in 1951. This dramatic decline, fueled by over pumping, rapid population growth, and exponentially increasing water demands, has created a water scarcity crisis in the country. India uses approximately 90 percent of fresh water sources for agriculture, one of the highest ratios in the world, and 60 percent of water use in agriculture originates from directly in?ltrated rainfall. Water scarcity, climate change, drought, floods, water delivery infrastructure at the rural level, extreme poverty, water-borne diseases, and water pollution are combined challenges that confront the Indian government and people.
How is rainwater harvesting having an impact? Studies indicate that water collection programs are having a profound impact in states like Gujarat and Rajasthan. An excellent example is found in the check dam movement in the parched Saurashtra region of Gujarat state. “This was a grassroots level movement that witnessed the formation of hundreds of village level institutions for organizing rainwater harvesting through planning, funding, and construction of a series of check dams as well as other rainwater harvesting structures in and around each village. The purpose was to collect and hold rainwater for a short time and recharge the underground aquifers, thereby bringing water to the open wells, most of which had run dry. From the late 1990s, such institutions have been formed in hundreds of villages in the region and the movement is reported to have had a signi?cant impact on water availability and agricultural incomes.”14
In Rajasthan state, remarkable rainwater harvesting and water restoration initiatives, under the dedicated leadership of Rajendra Singh and his NGO, Tarun Bharat Sangh (TBS), have brought vast improvements in water sustainability and water security for hundreds of thousands of citizens. Singh, who founded TBS in 1985, was awarded the Stockholm Water Prize in 2015. One of the main projects involved building johads, which are small, earthen check dams that capture and conserve rainwater, thus improving percolation and groundwater recharge. Since 1985, johads have been established in more than 650 villages in the Alwar district of Rajasthan. The Bhaonta village in Alwar district of Rajasthan was named India’s “most outstanding environmental community,” and received the 2000 Joseph C. John Award for its community projects to promote rainwater harvesting and forest protection. “The johads and a series of anicuts (small concrete dams) were built by the local community with support from Tarun Bharat Sangh (TBS), an Alwar-based NGO and Gram Vikas Navyuvak Mandal Laporiya (GVNML), a Jaipur-based NGO. This has resulted in a general rise of the groundwater level by almost six meters and a 33 percent increase in the forest cover in the area. Therefore, the local ingenuity, indigenous knowledge, and pride of the villagers have regenerated the local Bhaonta forest where the more elaborate and costly structures built by expert engineers have typically failed.”15
A detailed study of rain-fed irrigation in India’s agricultural sector reveals the extent of improvements that can be attained:
India ranks first among the rain-fed agricultural countries in terms of both extent (86 M ha) and value of produce. Farmers have started cultivating high-value crops which require intensive use of inputs, most importantly, life-saving irrigation. Frequent occurrence of midseason and terminal droughts of 1 to 3-weeks consecutive duration during the main cropping season are the dominant reasons for crop (and investment) failures and low yields. Provision of critical irrigation during this period has the potential to improve the yields by 29 to 114 per cent for different crops. A detailed district and agro-Eco regional level study, comprising 604 districts, showed that on a potential (excluding very arid and wet areas) rain-fed cropped area of 25 M ha, a rainfall surplus of 9.97 M ha was available for harvesting. A small part of this water (about 18%) was adequate to provide one critical irrigation application of 18.75 M ha during a drought year and 22.75 M ha during a normal year. Water used in supplemental irrigation had the highest marginal productivity and increases in rain-fed production above 50% were achievable. More specifically, net benefits improved by about 3-times for rice, 4-times for pulses and 6-times for oilseeds. Droughts appear to have limited impact when farmers are equipped with rainwater harvesting systems. Water harvesting and supplemental irrigation was economically viable at the national level and would have limited impacts downstream during normal years. This decentralized and more equitable intervention targeted resource-poor farmers and has the potential to serve as an alternative strategy to the proposed river linking and water transfer projects.16
Such results have played a role in 18 out of India’s 28 states, where rooftop rainwater harvesting is now mandatory on new buildings. A report by the Stockholm Environment Institute noted substantial rural and gender equality benefits in India through the application of rainwater harvesting. “In India, rainwater harvesting has been a successful starting point to put development on a positive track addressing both improved human well-being and re-generation of degraded landscapes, in particularly semi-arid and sub-humid zones. Through national watershed programs, key interventions in rainwater harvesting on farmland have increased household food supply and incomes. Rainwater harvesting in common areas of the landscape has improved ecosystem productivity of biomass, infiltration of rainfall to recharge shallow groundwater, and reduced soil erosion. In many cases, additional effects have been observed, including gender equality improvements, and general community strengthening and organization.”17
Rainwater harvesting offers an environmentally safe, cost-efficient, and effective approach to water scarcity and water-borne diseases. In many situations, it offers the most sensible solution. The challenges of unsafe water, unstable water sources, and problematic water collection often falls disproportionately hard upon women and children. Through water collection methods which have demonstrated efficient and ecological applications in rural communities in India, abundant new opportunities can be applied in water-insecure nations worldwide to successfully address significant water scarcity and health challenges.
- International Decade for Action ‘WATER FOR LIFE’ 2005–2015. United Nations Department of Economic and Social Affairs [online] (2014). http://www.un.org/waterforlifedecade/scarcity.shtml.
- Water Sanitation Health. World Health Organization [online] (2014). www.who.int/water_sanitation_health/diseases/en/.
- Roberts, AG. MIT Joint Program on the Science and Policy of Global Climate Change [online] (January 9, 2014). globalchange.mit.edu/pubs/all-reports.php.
- Progress on Sanitation and Drinking Water – 2015 Update and MDG Assessment 2015. WHO/UNICEF Joint Monitoring Programme for Water Supply and Sanitation [online] (2015). http://www.wssinfo.org/fileadmin/user_upload/resources/JMP-Update-report-2015_English.pdf.Human Development Report 2006: Beyond scarcity: power, poverty and the global water crisis. United Nations Development Program [online] (2006). http://hdr.undp.org/en/content/human-development-report-2006.
- Corcoran, E et al (eds). Sick Water? The central role of wastewater management in sustainable development. A Rapid Response Assessment. United Nations Environment Program, UN-HABITAT, GRID-Arendal [online] (2010). www.grida.no.
- International Decade for Action, Water for Life 2005-2015. UN Water [online] (2014). http://www.un.org/waterforlifedecade/background.shtml.
- Rahman, S et al. Sustainability of rainwater harvesting system in terms of water quality. The Scientific World Journal 2014, 721357 (2014).
- Gur, E & Spuhler, D. Rainwater harvesting (rural). SSWM [online] (2010). http://www.sswm.info/category/implementation-tools/water-sources/hardware/precipitation-harvesting/rainwater-harvesting-r.
- Thomas, TH & Martinson, DB. Roofwater harvesting: a handbook for practitioners. International Water and Sanitation Centre [online] (2007). https://www.gov.uk/dfid-research-outputs/roofwater-harvesting-a-handbook-for-practitioners.
- Lehmann, C, Tsukada, R & Lourete, A. Low-cost technologies towards achieving the millennium development goals: the case of rainwater harvesting. The International Policy Centre for Inclusive Growth, Bureau for Development Policy, UNDP and Government of Brazil [online] (2010). http://www.ipc-undp.org/pub/IPCPolicyResearchBrief12.pdf.
- Poverty and Equity Country Dashboard. World Bank [online] (2016). povertydata.worldbank.org.
- Kochhar, R. 10 projections for the global population in 2050. Pew Research Center [online] (February 3, 2014). http://www.pewresearch.org/fact-tank/2014/02/03/10-projections-for-the-global-population-in-2050/.
- Gandhi, VP & Bhamoriya, V. Rainwater harvesting for irrigation in India: potential, action, and performance [online] (2011). https://www.idfc.com/pdf/report/IIR-2011.pdf.
- Goyal, RR & Bhushan, B. Rainwater Harvesting: impact on society, economy and ecology. International Rainwater Catchment Systems Association [online] (2005). http://eng.warwick.ac.uk/ircsa/pdf/12th/2/Goyal-Radha.pdf.
- Blue Drop Series: Rainwater Harvesting and Utilization Rainwater Harvesting and Utilization (UN-HABITAT, Geneva, 2005) [online]. unhabitat.org/…/blue-drop-series-on-rainwater-harvesting-and-utilisation-book-3project.
- Stockholm Environmental Institute. Rainwater harvesting: a lifeline to human well-being. UN Water [online] (2009). http://www.unwater.org/downloads/Rainwater_Harvesting_090310b.pdf.