Availability of water is critical for ecosystem health and productivity, ensuring supply of a range of products and services, to benefit human well-being (e.g., GEO4, 2007; MA, 2005). Future pressures from climate change, growing population, rapid land use changes and already degraded water resource quality, may intensify water shortages in specific communities and exacerbate existing environmental and economic concerns (5). Population around the world today depends on the renewable resources of water for their water needs in industrial, agricultural and domestic sectors. But when these are withdrawals are greater than 20% of total renewable resources, water stress often is a limiting factor on development; withdrawals of 40% or more represents high stress. Similarly, water stress may be a problem if a country or region has less than 1,700 m3 yr-1 of water per capita (4). In 1990, approximately one-third of the world’s population lived in countries using more than 20% of their water resources, and by 2025 about 60% of a larger total would be living in such stressed countries, in the absence of climate change largely because of population growth (6).IPCC in its Third Assessment Report predicts that increase of temperature between 1-2°C would lead to decrease in water supply in regions already suffering from water scarcity such as the Mediterranean, southern Africa, and arid parts of central and south Asia affecting half a billion people. These areas will be further affected if the temperature increases 2-3 °C (1).
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With growing number of population belonging to the water stress areas of the world, it has become crucial for humans to find out alternative sources of water, proper management of the given resources and bring in technological changes to improve water use. Though centralized water management systems has a huge impact on our lives today, societies, government and citizens around the world are looking out of alternative resources to augment the available water resources. Rainwater harvesting, as one of such methods, is the accumulating and storing, of rainwater. Depending on local environmental conditions, water harvesting may provide a supplementary supply, an alternative supply or the only feasible improved supply. The current centralized water supply paradigm which is followed in all the cities of the world seems unsustainable and extremely high on energy consumption. In United States, about 4% of the U.S power generation is used for water supply to the population and electricity represents approximately 75 percent of the cost of municipal water processing and distribution (19) (20). As an alternative paradigm for more sustainable water availability, harvesting rainwater, storing it in tanks, and recharging groundwater may be used to provide drinking water, water for livestock, water for irrigation or to refill aquifers. In rural areas, rainwater can be used to even supplement agricultural income through small horticultural projects and maintaining improved amount of livestock apart from developing the quality of life of rural women in many parts of the world who spends a considerable portion of their day- to- day life in collecting water for drinking and house hold purposes. In just one day, more than 200 million hours of women’s time is consumed for the most basic of human needs – collecting water for domestic use (21)( I still remember, the distance I used to travel to collect water from nearby reservoirs as kid visiting my village during holidays back in India). As the civil society is becoming more aware and sensitized regarding its potential, rainwater harvesting can also be scaled up to neighborhood and micro-watershed levels.
More than one out of six people lack access to safe drinking water, namely 1.1 billion people, and more than two out of six lack adequate sanitation, namely 2.6 billion people (Estimation for 2002, by the WHO/UNICEF JMP, 2004). Rainwater collected from the roofs of houses, tents and local institutions, or from specially prepared areas of ground, can make an important contribution to drinking water. Rainwater systems are simple to construct from inexpensive local materials, and are potentially successful in most habitable locations. Roof rainwater can be of good quality and may not require treatment before consumption. Although some rooftop materials may produce rainwater that is harmful to human health, it can be useful in flushing toilets, washing clothes, watering the garden and washing cars; these uses amount to a significant amount of water used by a typical home. In many parts of the world, households and communities have augmented or substituted their household supplies with rainwater for reasons of scarcity, salinity, quality of service and for risk substitution. While rainwater may not always provide a full-year round of supply, it enhances water security in the house and generally provides a good quality water.
Historical development of rainwater harvesting
Water has been important for the development of cultural complexity in human society during the Holocene and earlier (16). Human ancestors have always used aquatic resources to their benefit (18), as we see the earliest association of hominid ancestors with lakes and pools dating back to 6 and 7 m.y. ago (Upper Miocene) from northern Chad, Central Africa(19).Rainwater collection is one of the oldest means of collecting water for domestic purposes. Archaeological excavations document ancient rainwater harvesting in Mesoamerica, the Mediterranean, and the Orient (10). Historically, in Baluchistan (erstwhile India and now in Pakistan), evidence of simple stone-rubble structures for impounding rainwater dates back to the third millennium BC (8). Hundreds of years before the birth of Christ, rainwater collection were already a common technique throughout the Mediterranean and Middle East, used by Egyptians, Palestinians, Iranians, Iraqis, Yemenis, Greeks and Romans(9). In the Negev desert in Israel, tanks for storing runoff from hillsides for both domestic and agricultural purposes have allowed habitation and cultivation in areas with as little as 100mm of rain per year.. Water was collected from roofs and other hard surfaces and stored in underground tanks, or excavated reservoirs (cisterns) with masonry domes (9). In some parts of the Middle East, rainwater was collected from hard surface areas and channeled through vertical shafts to horizontal tunnels (qanars) that in turn led the water to underground reservoirs (22). In addition to the traditional rainwater harvesting techniques found in India, North Africa and the western Mediterranean, there are also examples from Thailand, China, Bangladesh, Nepal, Sri Lanka, Indonesia and the small islands in the Pacific. In sub-Saharan Africa, the collection of rainwater was (and is) practiced using small containers, in among others, most of Southern Africa, Ghana, Kenya and Tanzania. The earliest known evidence of the use of the technology in Africa comes from northern Egypt, where tanks ranging from 200-2000m3 have been used for at least 2000 years – many are still operational today (7). Even in Western Europe, historical records show that in many places rainwater was the primary drinking water source for drinking water, the same applies to the Americas and Australia. In all three continents rainwater continues to be an important source for isolated homesteads and farms (11).
Rainwater harvesting for domestic water use in modern day
Though there is significant evidence of rainwater harvesting in the world historically, it was lost to people’s memory for sometime due to extensive water supply systems which came in place with the urbanization of the world. Potential for rainwater use is wide and there are many ways of capturing the rainwater runoff. In this paper, I would however like to focus more on the domestic usage of rainwater. Alternative sources of domestic water are becoming particularly important in urban areas of the world as urban population is rapidly increasing. Since 1950, the number of people living in urban areas has jumped from 750 million to more than 2.5 billion people. Currently, some 61 million people are added to cities each year through rural to urban migration, natural increase within cities, and the transformation of villages into urban areas(7). Due to the severe challenges of water stress and scarcity issues in the world today, these small stand alone techniques of water supply is becoming popular. Urbanization of the world has also changed the way houses are built worldwide and concrete roofing is providing good catchment areas closer to the domestic water users. Plastic and Ferro-cement tanks has also become a good alternative to earthen tanks as reliable, economic and durable means of water cisterns. Rapid urbanization of the cities around the world has also brought forward the faults of the water distribution systems in many parts of the world, especially in the developing countries where people have felt the need to become self sufficient in water supply within their means. As the quality and quantity of ground water is decreasing, rainwater is becoming an alternative source. Urbanization also is bringing together large number of people within smaller areas to live such has flats, apartments, residential complexes etc where rainwater harvesting is becoming a community based approach where the cost of implementation and the benefits are getting shared within the members of the communities.
Rainwater harvesting can be categorized in a number of different ways according to the type of catchment surface used and by implication the scale of activity. Essentially these are either rooftop, ground, or rock with rooftop being most suited to individual household or community water supply, while ground and rock being more geared towards agricultural irrigation. Conceptually, rainwater harvesting catchments can vary in size from the individual house to a river basin
Figure Source -http://buildandrebuild.com/rainwater-harvesting-and-you/
Rooftop rainwater harvesting however is a very small percentage of the total rainwater run-off. But as a small scale and domestic activity, this is significant as the production; control and use of these sources are maintained and controlled by domestic users. For arid and semi arid countries, rain-water is often the most readily accessible water source at the community and household level, although distribution of rainfall during the year, and storage necessary for the dry months can provide a problem. Rainwater collected using existing structures has few negative environmental impacts compared to other technologies for water resources development. Rainwater is relatively clean and the quality is usually acceptable for many purposes with little or even no treatment. The physical and chemical properties of rainwater are usually superior to sources of groundwater that may have been subjected to contamination. Rainwater harvesting can co-exist with and provide a good supplement to other water sources and utility systems, thus relieving pressure on other water sources. Rainwater harvesting provides a water supply buffer for use in times of emergency or breakdown of the public water supply systems, particularly during natural disasters. Rainwater harvesting can reduce storm drainage load and flooding in city streets. Users of rainwater are usually the owners who operate and manage the catchment system, hence, they are more likely to exercise water conservation because they know how much water is in storage and they will try to prevent the storage tank from drying up.Rainwater harvesting technologies are flexible and can be built to meet almost any requirements. Construction, operation, and maintenance are not labour intensive (7).Rainwater harvesting system also produce beneficial externalities in reducing peak storm water runoff and associated processing cost.
Rainwater harvesting as a sustainable water strategy
Access of water according to the UN is officially defined as 20 lpd within a 1 km distance from one’s dwelling. The UN considers this a minimal standard to which all countries, even low income ones, can aspire. This definition has been critiqued on two counts: (1) 1 km is a considerable distance, especially when carrying water, which is heavy. For many women and girls, who make up the great proportion of water carriers, fetching the family minimum could require several 1 km trips each way – a significant barrier to actual access. (2) Climatic variations are not accounted for in the universal definition of “access” (15). Rainwater harvesting can significantly address this issue and become a sustainable water source across the climatic condition if the management systems are robust and the water collected can be channelized to recharge groundwater. For example, Jordan faces a huge water crisis. Results of a study show that a maximum of 15.5 Mm3/y of rainwater can be collected from roofs of residential buildings provided that all surfaces are used and all rain falling on the surfaces is collected. This is equivalent to 5.6% of the total domestic water supply of the year 2005. The potential for water harvesting varies among the governorates, ranging from 0.023Ã-106 m3 for the Aqaba governorate to 6.45Ã-106 m3 for the Amman governorate. The potential for potable water savings was estimated for the 12 governorates, and it ranged from 0.27% to 19.7% (13).
Rainwater harvesting can also reduce the dependence on the centralized water supply systems. Mega-Cites worldwide are facing similar challenges of water scarcity and water stress like polluted freshwater resources, overexploited groundwater resources, insufficient or poorly maintained water supply infrastructure systems and insufficient technical and water management capacities (14).Small pockets of water resources within a city are more resilient and can draw on rainwater and groundwater, providing the city with greater flexibility in the face of water shortages, operational failures and natural disasters. History tells us that cultures do not give up until they have exhausted options for survival over the area they occupied for longer period. The Mayan civilization is a case in point, which developed around 3000 years ago in Mesoamerica, and faced recurrent droughts due to solar forcing before it collapsed due to climate deterioration towards the end of the Classic Period. Ancient reservoir technology developed by the Mayan people in the seasonally dry tropics of southern Maya lowlands reveals that rainwater storage was a major source of water supply during the dry season. Reservoirs were constructed, for example, in Tikal to cope with seasonal scarcity of water (16).
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Rainwater harvesting can also improve the situations of urban flooding. More land area around the world today is getting covered by asphalt and concrete as new roads are laid down to support increasing amount of transport use of urban population. This has lead to the lower seepage of surface water to replenish ground water resources. In the United States alone, pavements and other impervious surfaces cover more than 43,000 square miles-an area nearly the size of Ohio-according to research published in the 15 June 2004 issue of Eos, the newsletter of the American Geophysical Union. Collection of rainwater significantly reduces this stormwater to flow down the sewerage systems of a city. At times, this is effective in controlling urban flooding which happens when too much of water due to precipitation flows down the sewerage system which are not capable of handling the amount does not function properly.
Evidences and policies of successful rainwater harvesting around the world-
As the world tries out new methods to address the newer problems it face in solving natural resources scarcity issues and which in fact has been a significant factor for human civilization from time immemorial, rainwater harvesting experiments as a source of water is also happening worldwide. Currently there is no US agency that has focus on Rainwater Harvesting and states are rapidly doing their own thing. The H.R. 3598: Energy and Water Research Integration Act which has been passed by the House of Representative in December 2009 which is formulated to “to ensure consideration of water intensity in the Department of Energy’s energy research, development, and demonstration programs to help guarantee efficient, reliable, and sustainable delivery of energy and water resources”(32) may promote federal support in rainwater harvesting. Some states of Usa have significantly worked in promoting rainwater harvesting. In October of 2008, the city of Tucson, Arizona became the first municipality in the country to require developers of commercial properties to harvest rainwater for landscaping. The new measure – approved by a unanimous vote by the City Council – requires that new developments meet 50% of their landscaping water requirements by capturing rainwater. The new rule went into effect on June 1, 2010. Arizona taxpayers who install a “water conservation system” after January 1, 2007, and before January 1, 2012, may take a one-time tax credit of 25% of the cost of the system (up to a maximum of $1,000). This can be claimed over multiple tax years, but no taxpayer can receive more than a total of $1000 in credits through this program. Builders are eligible for an income tax credit of up to $200 per residence unit constructed with a water conservation system installed (17). Some government grants in Arizona also have given the scope of funding rainwater harvesting projects within an amount of $5000 (25). The Cincinnati EPA office has instituted a program to give incentives to homeowners for rain gardens or rain barrels to improve quality/timing of stormwater runoff, rather than promoting a central engineering solution. The City of Austin Water Conservation Program distributes over 250 rain barrels per month to homeowners at a subsidized cost, and provides rebates for the installation of approved cistern systems. Commercial/industrial properties can receive rebates up to $40,000 for the installation of rainwater harvesting and greywater systems. New commercial facilities must install a separate irrigation meter costing between $5,000 and $25,000 unless they can provide 100% of all outdoor water needs from alternate water sources such as rain, grey-water, and air conditioning condensate (26). With Clean River Rewards which is the storm-water utility’s discount program of Portland, helps ratepayers save money and work for clean rivers and healthy watersheds at the same time through storm-water management in individual properties. There is an 100percent discount on the onsite storm-water management charges because these actions helps protect the rivers, streams and the groundwater(27).Rainwater harvesting methods are used as sources of water supply in other parts in USA and more and more state governments are coming out to give this method a try. In California, the California Rainwater Capture Act of 2010, would authorize a landowner to install, maintain, and operate, on the landowner’s property, a rainwater capture system meeting specified requirements. The bill is also known as AB 1834 (35).In California however there is no tax credit given to the people in order to install rainwater harvesting equipments. In New Mexico however there is no mandatory law to install rainwater harvesting in individual houses, but there is a tax credit for NEW Green Buildings, which could include rainwater harvesting. For Build Green New Mexico “Gold level”, the maximum possible credit is $11,000.00 per house. The North Carolina Department of Environment and Natural Resources, Division of Soil and Water has implement Community Conservation Assistance Program has created a voluntary incentive based program for promoting rainwater harvesting and awareness generation educational programmes are in place, yet there is no tax incentives in place. Under this program the landowner may be reimbursed up to 75 percent of the pre-established average cost of the BMP (best management practices). Included in this program are Rainwater Harvesting Systems (36) (37) (38).
Around the world, rain water harvesting has many success stories. In Singapore, rainwater harvesting is growing as rapid urbanization is inducing rapid water demand. In Changi Airport, rainwater is collected from the runways which are used primarily for non-potable functions such fire-fighting drills and toilet flushing. Such collected and treated water accounts for 28 to 33% of the total water used, resulting in savings of approximately S$ 390,000 per annum. In India, direct recharge of rainwater into the ground (40) resulted in groundwater level increases of up to 5 to 10 metres in just two years. Water scarcity problems in Indonesia, has made government introduce a regulation requiring that all buildings have an infiltration well. The regulation applies to two-thirds of the territory, including the Special Province of Yogyakarta, the Capital Special Province of Jakarta, West Java and Central Java Province. It was estimated that if each house in Java and Madura had its own infiltration well, the water deficit of 53% by the year of 2000 would be reduced to 37%, which translates into a net savings of 16% through conservation. UNICEF is working with communities in Alor in Indonesia and the communities has a very positive response towards this effort (39).In Tokyo, Japan rainwater and reclaimed waste water is used to address water demand in emergency cases. There are 850 facilities for rainwater use in Tokyo. Since reclaimed wastewater use has several benefits, a huge water volume has been utilized for various purposes such as washing; water-cooling, toilet flushing, waterway restoration and creation of recreational waterfront (30).There are many case studies and success stories, feasibility studies on rainwater harvesting methods and uses in the world today. An exhaustive list of all of them is beyond the scope of this paper. International organization for promoting sustainable environmental strategies like UNEP are growingly focusing on this method as to cater water needs of communities to attain the objectives of Millennium Development Goals. Poorer countries in Africa and Asia are experimenting on harvesting rainwater for various human uses for a long time now in order to answer some of the persistent water problems plaguing human lives in these continents.
Evaluation of rainwater harvesting as a water resource-
As rainwater harvesting is emerging in many regions of the world as a sustainable means of addressing short term and long term water scarcity, it is critical to understand the robustness of the system. Purity of rain water is in question when there are instances of acid rain all around the world. Growing air pollution in urban areas also pollute the rain before it falls and therefore rainwater harvesting requires treatment mechanism to make the water fit for human consumption. Rainfall intensity and the number of dry days preceding a rainfall event significantly affects the quality of run-off water from the catchment systems. Presence of fecal coli form and other microbiological contaminants, zinc concentration due to the material used in roofing are some of the shortfalls of rainwater harvesting (41). Household water management practices where rainwater is used as non-potable household use and the limited water supplied by the central water service system as potable water source can be a good alternative. Newer technological developments can easily solve these problems of contaminants in rainwater though it may significantly increase the cost of the water. Household level water catchment areas are often small and it is increasingly smaller when we think of urban areas. Moreover, as people around the world prefer to stay apartments, access to individual roofs for each water consumer is impossible. But this also gives the scope of community involvement and shares the cost. Small involvements like managing a rainwater catchment in a building can bring in greater differences in how people think about the water availability. It becomes educational and it brings in awareness which translates in how we look towards the way we use water in our daily lives. People understands solutions of the problems they face better than analysis of their problem, when solutions are within their reach, they implement them. In the evolution of human civilization, it can be studied that humans have addressed their needs in small measures which together as brought in changes in they we live out life today.
Popularizing rainwater harvesting requires significant push by the governmental institution. Water till date is used as a free good in many parts of the world and people generally do not have the mental set up to invest for water services and thinks that it is the responsibility of the government. Interestingly in some states of USA like Utah, Colorado and Washington, catching rain water was against the law as it reduces the water catchment area for downstream users if water is taken in up stream. Rainwater harvesting was possible in these states if the individual user goes through the process of gaining a state water right. With the growing problems of water scarcity in these regions, governments are slowly taken small yet bold steps in legalizing rain water harvesting by domestic users. Colorado is taking baby steps towards legalizing rainwater collection. Senate Bill 80 was signed by the Governor on 4/22/09 and becomes law on July 1, 2009. It allows rural catchment (Senate Bill 80), but still has some hurdles for those that want to move forward (42). The Department of Ecology of the State of Washington, on October 12, 2009 issued an Interpretive Policy Statement clarifying that a water right is not required for rooftop rainwater harvesting (43). In Utah, the state passed Senate Bill 32 in 2010 which permits rainwater catchment for maximum capacity of no more than 2,500 gallons. There are several other restrictions, but the state engineer must grant the permit if all the conditions are met. In countries, around the world especially India and China which are experiencing rapid industrial developments, rainwater harvesting is also becoming a feasible policy advice. In the 11 Five Year Plan of the Government of India, rainwater harvesting is taken into consideration where sources of groundwater are limited. The plan stress that restoration and building of tanks and other water bodies along with rainwater harvesting structures for recharge and for direct collection at community and household levels constitute an attractive option. The Central Government should support the states for tapping the maximum external assistance for this purpose, a part of the assistance could be shared by the Centre as decided in the case of the external assisted Water Bodies Restoration Programme wherein 25% grant of the project cost is passed on to the states (45). The Water law of the People’s Republic of China was promulgated on Oct.1 2002, This is the law concerning the water resources in a national scope, which pointed out definitely: “the national government encourages citizens to use rainwater and tiny salt water for the purposes of harvesting, exploitation and utilization in regions short of water resources.”(46) For promoting the development of rainwater utilization, the National Construction Department announced the Chinese ecosystem residence technique valuation manual in 2001 and updated it three times in the following three years, each edition formulating content about rain water utilization (47).
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