Rainwater Harvesting (RWH) is a method of collecting and conserving surface runoff rain water for storage and use or for groundwater recharge. RWH has been in practice for centuries but gross misuse of existing water sources has led to global awareness and its increased importance off-late. Though simple in principle, numerous variables come into play while implementing an efficient RWH system (climate, humidity, temperature, rainfall pattern, finances etc.).
The contents of this factsheet are results of the Indo-European Project NaWaTech- “Natural Water Systems and Treatment Technologies to cope with Water Shortages in Urbanised Areas in India”, co-financed by the EC and the DST – India.
Design and Construction Principles
All designs of RWH systems basically include: (A) rain, (B) catchment area (roof, pavement area, storm drains etc.), (C) conveyance system (gutters, down pipes), (D) storage units or tanks (over ground / underground) and (E) distribution system (pipelines, pumps). In addition, there are some complementary units like filter/screens, first-flush diverters, disinfection methods (chlorination, boiling, UV) and overflow management pipes to complete the RWH system (CSE 2013). The “Rational Method” states that Potential Rainwater Harvested = Rainfall (mm/year) x Catchment area (m2) x Runoff Coefficient; run-off coefficient is defined as amount of water that runs-off the catchment area and can be collected relative to the amount of rainwater that it actually receives. It differs case-wise depending on surface of the catchment area (THOMAS & MARTINSON 2007). Keeping in mind the above, some construction guidelines are: (1) Catchment Area: use of paints, heavy metals, tiles for coating should be conscientious; (2) Gutters PVC or G.I: non-corrosive & sturdy, width of the gutters based on catchment area; (3) Filters/Screens: coarse mesh (5 mm) or fine mesh (0.4 mm); first-line defenceto protect water quality; (4) Storage tanks (RCC, ferrocement, plastic, etc.): size depends on many factors like amount of rainfall, no. of end users, cost etc. (CEHI 2009).
Operation and Maintenance
Periodic inspection of the RWH system is imperative to preserve quality, reduce contamination and ensure full use of the system. It does not require skilled labour. Cleaning of catchment areas before the start of every rainy season is the normal practice. Also annual inspection and cleaning of the storage tank, gutters, down-pipes and filters (3 to 6 months) is sufficient (KHOURY-NOLDE n.y). Repair of broken/cracked storage tanks tops the priority list. Disinfection of the stored water should be carried out periodically, if it is used for potable purposes.
RWH is site specific and it is difficult to give an overall cost for it. Rain and catchment area are free of cost, especially if RWH is integrated ab initio, but varying capital and O & M costs are incurred for the conveyance system (downpipes, gutters, filters/screens), which can be brought down by diligent work plans. Majorly, the storage tank occupies 30-70% of the total costs. A study in Andhra Pradesh (India) put the cost of constructing RWH at Rs 1.30 / litre / household (BABU 2005). Elsewhere, the U.S. Environmental Protection Agency report construction cost at approx. $4 - $6 / gallon / person (EPA 2013) (1 gallon= 3.78 L).
Experiences in Europe and other Cities of the World
Adapted from Global Water Partnership – Mediterranean 2013
The Mediterranean islands, among the most arid regions in the world with limited freshwater resources depend heavily on desalination and water transfer and have recently adapted to the RWH technology for tackling their water issues. The region is more prone to issues such as water scarcity and extreme weather events with a heavy impact on freshwater availability in terms of quantity and quality. To demonstrate and educate people towards a “new water culture” necessary for addressing the current and future water scarcity challenges, a Non-Conventional Water Resources (NCWR) Programme was implemented in 2008 by the Global Water Partnership – Mediterranean (GWP-Med) and partner institutions (including the Ministries of Greece & Mozo) with companies like Coca Cola as a key collaborators primarily targeting the Grecian and Maltese islands. It aims at advancing the use of NCWR and in revitalising and reintroducing traditional RWH combined and improved with innovative techniques and methods in those islands to secure water availability and facilitate sustainable development. Also included are software activities like awareness generation, capacity building and trainings. The soaring success of the programme has resulted in successful implementation of new RWH systems and rehabilitation of old systems numbering 50 RWH demonstration projects in toto for public buildings in 19 Mediterranean islands till the start of 2013. This has culminated in a combined annual yield of approx. 8 million litres of water along with training of thousands of student’s teachers and technicians on RWH.
Experiences in India
Rainwater harvesting in South Asia differs from that in many parts of the world in that it has a history of continuous practice for at least the last 8000 years. However, it matters more today than ever before (PANDEY et al. 2003). Many reasons typical to a developing economy like diminishing fresh water sources, decline in the groundwater tables, low productivity of wells, climate changes and exponential human population growth have been responsible for an attempt to search sustainable and renewable water sources in India. In June 2001, the Ministry of Urban Affairs and Poverty Alleviation made RWH mandatory in all new buildings with a roof area of more than 100 m2 and in all plots with an area of more than 1000 m2 that were being developed (Legislation on RWH CSE 2013). Further, under the Jawaharlal Nehru National Urban Renewal Mission targeting formation of environmentally sustainable cities, a directive was issued to all the Urban Local Bodies for amending their building by-laws and making RWH mandatory (MoUD India). Accordingly in 2007, the BMC Mumbai made it compulsory for buildings with plot areas of 300 m2 to have RWH system. Similarly other cities like Chennai, Bangalore, Thrissur, Hyderabad, Pune and Nagpur have also made RWH mandatory for new constructions. Very recently, East Delhi has decided to join the bandwagon by making prerequisite for all households of 27 m2 or above (as against 84 m2 previously) to have water conservation facility (DECCAN HERALD 2013). The obvious advantages conferred by the technology are seen to be percolating positively among people. Many success stories are seen arising from the village backdrop since there is no municipal water supply as a backup option upon depletion of ground water reserves and therefore villagers have started being proactive towards conservation of rainwater to tackle times of crisis. Unlike the village scenario, the urban population faces a crunching need, i.e. space constraints. However some successful urban projects of RWH are described below:
Panchsheel Park Colony, Delhi: In a benchmark achievement, the society invested Rs. 0.8 million (USD 20,000) to secure RWH for all the plots in the colony. From the total roof and surface area of 357,150 m2 receiving rainfall (611 mm/year), 174,575 m3 rainwater was harvested in 2002 resulting in a total rise of 0.7 m of groundwater level in the area (UN-HABITAT 2005).
Aizawl, Mizoram: At present, Aizawl has more than 10,000 RWH tanks in individual houses, which have been constructed by the residents at their own expense or with state government assistance. Rainfall in Mizoram (average 2,500 mm/year) is distributed throughout the year. Most of the buildings are constructed with sloping roofs that use Corrugated Galvanised Iron (CGI) sheets, which are conducive to RWH. Rain gutters (PVC pipes / bamboo) are used to drain water into the cylindrical storage tanks with GI semi-circular rain gutters to catch rainwater. Gradually, reinforced cement concrete (RCC), ferrocement and plastic tanks are being introduced (roughly averaging 10,000 litres capacity). In a pollution-free state like Mizoram where major industries are yet to come, rainwater is free from undesirable chemicals and is of potable quality (UN-HABITAT 2005).
In spite of these advances, the situation continues to be critical. Maharashtra is currently facing the worst drought conditions in 40 years with 11,801 villages in 15 districts declared as drought-affected and millions of people migrating towards the cities in a huge exodus (IBTL 2013). Also a recent study by Observer Research Foundation claimed that RWH in Mumbai was a ‘joke’ with many new buildings not following the above guidelines and with many existing RWH systems being non-functional (TOI 2013). By adhering to state guidelines, conscientious implementation of RWH systems and diligent O & M one can definitely overcome obstacles and help the country move towards a more sustainable model of water management.
For more information please visit: (Rainwater Harvesting)
The research leading to these results has received funding from the European Union Seventh Framework Programme ([FP7/2007-2013]) under Grant Agreement N°  and the Department of Science and Technology of the Government of India DS.O DST/IMRCD/NaWaTech/ 2012/(G).
Rain Water Harvesting is the age old traditional practice which is being practiced from the birth of human civilization. Like other living organisms man cannot survive without water. This made him to think and invent on different types of harvesting structures in order to obtain potable water. From the decades onwards with new technologies and globalization the structures focused are on dams, reservoirs, canals, irrigation tanks, percolation tanks etc. But, with the increasing population (human and animal) and with diseases related to water, it has become incessant practice to provide safe drinking water. In continuation to this above practice, a project on Roof top rain water harvesting structure with a study was implemented to provide safe drinking water to the community and to identify the best possible technology with respect to the specific region. In this paper, it covers the components that can be taken under the rain water harvesting structure, geographical area, availability of the water quantity, its quality and water demand. It also covered about the design parameters in which the flexibility and community management can promote and accordingly the design was modified. The main conclusion of this paper was the acceptance of the community about the technology, its design considerations and about the promotion of this technology in the water scarcity and pollutant regions. Finally, the study revealed that, it requires awareness (Psychological awareness) about the utilization of direct rain water with a primary filter unit, challenge of social and community acceptance, maintenance and time involvement for effective utilization and the water available at the door step with an amount of Rs. 1.30/- per liter.BABU, A. (2005): Roof Top RWH System in Deccan Plateau Region, Andhra Pradesh, India.. 12th International Rainwater Catchment Systems Conference. New Delhi: URL [Accessed: 16.03.2015]
A practical guideline featuring best practices for rainwater harvesting in small Island Caribbean environmentsCEHI (2009): Rainwater - Catch it While You Can. A Handbook on Rainwater Harvesting in the Carribean. Nairobi: United Nations Environment Programme (UNEP) URL [Accessed: 16.03.2015]
CSE’s special website, rainwaterharvesting.org, provides interested people comprehensive information on rainwater harvesting – on water crisis, conflicts, solutions, technologies, water crusaders and policy, including a database of different technologies for rural and urban contexts. To provide information on resource persons and experts, CSE has compiled a database of NGOs and individuals knowledgeable about water harvesting across the country.CSE (n.y): What is Rainwater Harvesting?. New Delhi: Centre for Science and Environment (CSE) URL [Accessed: 09.04.2013]
As a part of the Centre for Science and Environment's (CSE) campaign to spread awareness about community based rainwater harvesting techniques, the centre has identified Sixteen model projects in Delhi, from among those that have been designed by it. CSE has helped in the process of implementation of these and has been monitoring their impact on a regular basis. These Sixteen model projects have been constructed by enterprising citizens who sought CSE's help to setup rainwater harvesting structures in their colonies and institutions. The structures have a distinctive geographical and geological characteristic; the Mira Model School model, for example, has been constructed on a sedimentary terrain and the Shri Ram School project is on a hilly terrain. They also feature different forms of rainwater harvesting - rooftop harvesting and surface water harvesting.CSE (n.y): Model Projects for Urban RWH. New Delhi: Centre for Science and Environment (CSE) URL [Accessed: 13.04.2013]
Rainwater harvesting has been used throughout history as a water conservation measure, particularly in regions where other water resources are scarce or difficult to access. In recent years, researchers and policy makers have shown renewed interest in water use strategies due to rising water demand, increased interest in conservation (both water and energy), and an increased regulatory emphasis on reducing storm water runoff volumes and associated pollutant loads. In the last decade, as interest in the practice has grown, numerous state, municipal, and regional agencies have adopted or amended codes and guidelines to encourage responsible and effective rainwater harvesting practices. In addition, researchers from universities and non-government organizations, as well as industry consultants, have published papers and articles addressing a broad range of topics related to the installation, maintenance, costs, and performance of harvest and use systems. A literature review of existing research and policy documents related to rainwater harvesting has been conducted, with particular focus on characterizing the current state of the practice in the areas of: (1) water conservation, (2) storm water volume and pollutant load reduction, (3) code and administration considerations and (4) cost factors. The purpose of this report is to summarize the existing knowledge base in these four areas, assess factors affecting economic benefits of rainwater harvesting, and identify topics requiring additional research. This report is not intended to serve as a design document. Readers looking for design guidance should consult a more technically-focused publication, such as the Texas Manual on Rainwater Harvesting (TWDB, 2005).EPA (2013): Rainwater Harvesting - Conservation, Credit, Codes, and Cost Literature Review and Case Studies. Washington: United States Environmental Protection Agency (EPA) URL [Accessed: 16.03.2015]
The Maltese Islands have limited freshwater resources and depend heavily on desalination. Therefore there is an evident need to mobilise non conventional Water Resources (NCWR) in order to secure water availability and facilitate sustainable development.GWP-Med (2011): Non Conventional Water Resources Programme in Malta (Alter Aqua). Global Water Partnership - Mediterranean (GWP-Med) URL [Accessed: 13.04.2013]
The worst ever drought that the state of Maharashtra has experienced till date is the 1972 drought when almost 5 million people had no work as the crops failed. But the current drought in Maharashtra is set to break all the records. With millions estimated to be affected, lakhs of cattle rendered hungry without fodder, this drought is the worst kind of natural disaster that the state has faced. Almost 1/5th of Maharashtra is reeling under drought.IBTL (2013): Maharashtra Drought 2013. New Delhi: India - Behind the Lens (IBTL) URL [Accessed: 13.04.2013]
Rainwater harvesting is a technology used to collect, convey and store rain for later use from relatively clean surfaces such as a roof, land surface or rock catchment. The water is generally stored in a rainwater tank or directed to recharge groundwater. Rainwater infiltration is another aspect of rainwater harvesting playing an important role in stormwater management and in the replenishment of the groundwater levels. Rainwater harvesting has been pr acticed for over 4,000 years throughout the world, acticed for over 4,000 years throughout the world, traditionally in arid and semi-arid areas, and has provided drinking water, domestic water and water for livestock and small irrigation. Today, rainwater harvesting has gained much on significance as a modern, water-saving and simple technology.KHOURY-NOLDE, N. (n.y): Rainwater Harvesting. Germany: Zero-M & Fachvereinigung Betriebs- und Regenwassernutzung e.V. URL [Accessed: 16.03.2015]
Extreme climate events such as aridity, drought, flood, cyclone and stormy rainfall are expected to leave an impact on human society. They are also expected to generate widespread response to adapt and mitigate the sufferings associated with these extremes. Societal and cultural responses to prolonged drought include population dislocation, cultural separation, habitation abandonment, and societal collapse. A typical response to local aridity is the human migration to safer and productive areas. However, climate and culture can interact in numerous ways. We hypothesize that people may resort to modify dwelling environments by adapting new strategies to optimize the utility of available water by harvesting rain rather than migrating to newer areas. We review recent palaeoclimatological evidence for climate change during the Holocene, and match those data with archaeological and historical records to test our ‘climate change–rainwater harvest’ hypothesis. We find correlation between heightened historical human efforts for construction of rainwater harvesting structures across regions in response to abrupt climate fluctuations, like aridity and drought. Historical societal adaptations to climate fluctuations may provide insights on potential responses of modern societies to future climate change that has a bearing on water resources, food production and management of natural systems.PANDEY, D.N. GUPTY, A.K. ANDERSON, D.M (2003): Rainwater Harvesting as an Adaptation to Climate Change. (= Current Science , 1 / 85 ). Bengaluru: Current Science URL [Accessed: 16.03.2015]
This handbook has been written to assist NGO and government staff responsible for implementing domestic roofwater harvesting systems or programmes. It can be used to design single roofwater harvesting systems. The handbook focuses primarily on low-cost DRWH in the ‘humid tropics’ (areas close to the Equator with average rainfall over 800 mm).THOMAS, T.H. MARTINSON, D.B. (2007): Roofwater Harvesting: A Handbook for Practitioners. Delft: IRC International Water and Sanitation Centre URL [Accessed: 12.03.2019] PDF
MUMBAI: Most new buildings in the city do not have a functional rainwater harvesting system though it is mandated by law, said a report released by a think tank on World Water Day on Friday. It was also found that the city wastes over 900 million litres of water every day, more than the daily water supply to Pune city. Experts brought together by the Observer Research Foundation (ORF) said the severe drought in 16 districts of the state should serve as a wake-up call to the city. They urged residents and local bodies to adopt sustainable solutions to save the city from the acute water crisis in the rest of the state.TOI (2013): Rainwater Harvesting a Joke in Mumbai, Finds Study. India: Times of India (TOI) URL [Accessed: 17.03.2013]
The Blue Drop Series on Water Harvesting and Utilisation is divided into three and each one has a specific target group- policy makers, beneficiaries and capacity and implementing agencies. The publications give an overview of the concept of rainwater and have a focus on the legal and administrative framework for rainwater harvesting. Book 2: Beneficiaries & Capacity.UN-HABITAT (2005): Rainwater Harvesting and Utilisation. Blue Drop Series, Book 2: Beneficiaries & Capacity. Nairobi: UN-Habitat URL [Accessed: 12.03.2019] PDF
The rapid development of cities and consequent population explosion in urban areas has led to depletion of surface water resources. For fulfillment of daily water requirement, indiscriminate pumping of ground water is being resorted to, leading to lowering of ground water table. At the same time the rain water is not being conserved which ultimately goes waste. To avoid this imbalance, conservation of rain water in the form of rain water harvesting is the only solution. Rain water harvesting can be effectively implemented in our office and residential complexes for conservation of rain water. The subject has assumed lot of significance in the present scenario. This has been included in Indian Railway Works Manual 2000 vide correction slip no. 10 dated 17.02.05 also. This publication is an attempt to compile all the relevant Information regarding various methods commonly in use. These methods can be used by field engineers for designing and implementing Rain Water Harvesting systems.IRICEN (2006): Rain Water Harvesting. Pune: Indian Railways Institute of Civil Engineering (IRICEN) URL [Accessed: 16.03.2015]
Compendium of Natural Water Systems and Treatment Technologies to cope with Water Shortages in Urbanised Areas in India
The Compendium of NaWaTech Technologies presents appropriate water and wastewater technologies that could enable the sustainable water management in Indian cities. It is intended as a reference for water professionals in charge of planning, designing and implementing sustainable water systems in the Indian urban scenario, based on a decentralised approach.BARRETO DILLON, L. ; DOYLE, L. ; LANGERGRABER, G. ; SATISH, S. ; POPHALI, G. (2013): Compendium of Natural Water Systems and Treatment Technologies to cope with Water Shortages in Urbanised Areas in India. Berlin: EPUBLI GMBH URL [Accessed: 11.12.2015]