the type of technology used. governmental aid and ngos can assist communities facing poverty by providing the materials and education necessary to develop and maintain rwh setups. some studies show that rainwater harvesting is a widely applicable solution for water scarcity and other multiple usages, owing to its cost-effectiveness and eco-friendliness. constructing new substantial, centralized water supply systems, such as dams, is prone to damage local ecosystems, generates external social costs, and has limited usages, especially in developing countries or impoverished communities. on the other hand, installing rainwater harvesting systems is verified by a number of studies to provide local communities a sustainable water source, accompanied by other various benefits, including protection from flood and control of water runoff, even in poor regions. rainwater harvesting systems that do not require major construction or periodic maintenance by a professional from outside the community are more friendly to the environment and more likely to benefit the local people for a longer period of time. thus, rainwater harvesting systems that could be installed and maintained by local people have bigger chances to be accepted and used by more people. the usage of in-situ technologies can reduce investment costs in rainwater harvesting. in-situ technologies for rainwater harvesting could be a feasible option for rural areas since less material is required to construct them. they can provide a reliable water source that can be utilized to expand agricultural outputs. above-ground tanks can collect water for domestic use; however, such units can be unaffordable to people in poverty. limitations rainwater harvesting is a widely used method of storing rainwater in the countries presenting with drought characteristics. several pieces of research have derived and developed different criteria and techniques to select suitable sites for harvesting rainwater. some research was identified and selected suitable sites for the potential erection of dams, as well as derived a model builder in arcmap 10.4.1. the model combined several parameters, such as slope, runoff potential, land cover/use, stream order, soil quality, and hydrology to determine the suitability of the site for harvesting rainwater. harvested water from rwh systems can be minimal during below-average precipitation in arid urban regions such as the middle east. rwh is useful for developing areas as it collects water for irrigation and domestic purposes. however, the gathered water should be adequately filtered to ensure safe drinking. quality of water rainwater may need to be analyzed properly, and used in a way appropriate to its safety. in the gansu province, for example, solar water disinfection is used by boiling harvested rainwater in parabolic solar cookers before being used for drinking. these so-called "appropriate technology" methods provide low-cost disinfection options for treatment of stored rainwater for drinking. while rainwater itself is a clean source of water, often better than groundwater or water from rivers or lakes, the process of collection and storage often leaves the water polluted and non-potable. rainwater harvested from roofs can contain human, animal and bird feces, mosses and lichens, windblown dust, particulates from urban pollution, pesticides, and inorganic ions from the sea (ca, mg, na, k, cl, so4), and dissolved gases (co2, nox, sox). high levels of pesticide have been found in rainwater in europe with the highest concentrations occurring in the first rain immediately after a dry spell; the concentration of these and other contaminants are reduced significantly by diverting the initial flow of run-off water to waste. improved water quality can also be obtained by using a floating draw-off mechanism (rather than from the base of the tank) and by using a series of tanks, withdraw from the last in series. prefiltration is a common practice used in the industry to keep the system healthy and ensure that the water entering the tank is free of large sediments. a concept of rainwater harvesting and cleaning it with solar energy for rural household drinking purposes has been developed by nimbkar agricultural research institute. conceptually, a water supply system should match the quality of water with the end-user. however, in most of the developed world, high-quality potable water is used for all end uses. this approach wastes money and energy and imposes unnecessary impacts on the environment. supplying rainwater that has gone through preliminary filtration measures for non-potable water uses, such as toilet flushing, irrigation, and laundry, may be a significant part of a sustainable water management strategy. rainwater cisterns can also act as habitat for pathogen-bearing mosquitoes. as a result, care must be taken to ensure that female mosquitoes can not access the cistern to lay eggs. larvae eating fish can also be added to the cistern, or it can be chemically treated. research the south african water research commission has supported research into rainwater harvesting. studies in arid, semiarid, and humid regions have confirmed that techniques such as mulching, pitting, ridging, and modified run-on plots are effective for small-scale crop production. hydrofracturing has regularly been used to improve the performance of water boreholes. from 1990 to 1992, 170 boreholes had been hydrofractured. country examples canada this section is an excerpt from rainwater harvesting in canada. a small rainwater harvesting tank in quebec. rainwater harvesting is becoming a procedure that many canadians are incorporating into their daily lives, although data does not give exact figures for implementation. rainwater can be used for a number of purposes including stormwater reduction, irrigation, laundry and portable toilets. in addition to low costs, rainwater harvesting is useful for landscape irrigation. many canadians have started implementing rainwater harvesting systems for use in stormwater reduction, irrigation, laundry, and lavatory plumbing. provincial and municipal legislation is in place for regulating the rights and uses for captured rainwater. substantial reform to canadian law since the mid-2000s has increased the use of this technology in agricultural, industrial, and residential use, but ambiguity remains amongst legislation in many provinces. bylaws and local municipal codes often regulate rainwater harvesting. multiple organizations and companies have developed in canada to provide education, technology, and installation for rainwater harvesting. these include the canadian association for rainwater management (canarm), canadian mortgage and housing corporation (cmhc), and cleanflo water technologies. canarm is an association that prioritizes education, training and spreading awareness for those entering the rainwater harvesting industry. india this section is an excerpt from water supply and sanitation in india § rainwater harvesting. in the early 21st century, india began heavily investing in rainwater harvesting infrastructure and policy as an urgent response to water scarcity. in 2001, tamil nadu became the first indian state to make rainwater harvesting compulsory in every building to avoid groundwater depletion. in rajasthan, rainwater harvesting has traditionally been practiced by the people of the thar desert. increase in rainwater harvesting efforts across the nation have revived ancient water harvesting systems in rajasthan, such as the chauka system from the jaipur district. other large cities like pune, mumbai and bangalore all have varying rules for mandatory rainwater harvesting, especially in new buildings. in 2002, the municipal corporation of greater mumbai required all new buildings over 1000 square meters to have rainwater harvesting infrastructure. the law was expanded in 2007 to 300 square meters. the goal was to ensure buildings had enough water to last them through non-monsoon seasons. the process included a catchment system, an initial flush, and extensive filtering. as of 2021, the brihanmumbai municipal corporation (bmc) reported 3000 newly constructed or redeveloped buildings with rainwater harvesting infrastructure. however, many residents have complained that the stored water is contaminated, turning saline and brackish. experts and residents argue that bmc authorities have done little to take implementation seriously, and the actual effectiveness of the rainwater harvesting mandate is unknown. while rainwater harvesting in an urban context has gained traction in recent years, evidence points toward rainwater harvesting in rural india since ancient times. united kingdom this section is an excerpt from rainwater harvesting in the united kingdom. rainwater harvesting in the united kingdom is a practice of growing importance. rainwater harvesting in the uk is both a traditional and reviving technique for collecting water for domestic uses and is generally used for non-hygienic purposes like watering gardens, flushing toilets, and washing clothes. in commercial premises like supermarkets it is used for things like toilet flushing where larger tank systems can be used collecting between 1000 and 7500 litres of water. it is claimed that in the south east of england there is less water available per person than in many mediterranean countries. rainwater is almost always collected strictly from the roof, then heavily filtered using either a filter attached to the down pipe, a fine basket filter or for more expensive systems like self-cleaning filters placed in an underground tank. uk homes using some form of rainwater harvesting system can reduce their mains water usage by 50% or more, although a 20-30% saving is more common. at the present time (depending upon where you live in the uk) mains water delivery and equivalent waste water and sewerage processing costs about £2 per cubic metre. reducing mains-water metered volumes also reduces the sewerage and sewage disposal costs in the same proportion, because water company billing assumes that all water taken into the house is discharged into the sewers. united states this section is an excerpt from water supply and sanitation in the united states § rainwater harvesting. in the united states, until 2009 in colorado, water rights laws almost completely restricted rainwater harvesting; a property owner who captured rainwater was deemed to be stealing it from those who have the rights to take water from the watershed. now, residential good owners who meet certain criteria may obtain a permit to install a rooftop precipitation collection system (sb 09-080). up to 10 large scale pilot studies may also be permitted (hb 09-1129). the main factor in persuading the colorado legislature to change the law was a 2007 study that found that in an average year, 97% of the precipitation that fell in douglas county, in the southern suburbs of denver, never reached a stream—it was used by plants or evaporated on the ground. rainwater catchment is mandatory for new dwellings in santa fe, new mexico. texas offers a sales tax exemption on the purchase of rainwater harvesting equipment. both texas and ohio allow the practice even for potable purposes. oklahoma passed the water for 2060 act in 2012, to promote pilot projects for rainwater and graywater use among other water-saving techniques. other countries rainwater harvesting tank in rwanda. uganda: rainwater harvesting has been used in uganda to promote household and community scale water security for many years. regular maintenance is an ongoing challenge with existing installation and there are many examples of installations that have failed due to poor maintenance. research has also shown that awareness of rwh and how to access necessary resources to implement rwh is variable across ugandan society. thailand has the largest fraction of the population in the rural area relying on rainwater harvesting (currently around 40%). rainwater harvesting was promoted heavily by the government in the 1980s. in the 1990s, after government funding for the collection tanks ran out, the private sector stepped in and provided several million tanks to private households, many of which continue to be used. this is one of the largest examples of self-supply of water worldwide. in bermuda, the law requires all new construction to include rainwater harvesting adequate for the residents. new zealand has plentiful rainfall in the west and south, and rainwater harvesting is the normal practice in many rural areas, using roof water directed by spouting into covered, 1000 litre storage tanks, with the encouragement of most local councils. in sri lanka, rainwater harvesting has been a popular method of obtaining water for agriculture and for drinking purposes in rural homes. the legislation to promote rainwater harvesting was enacted through the urban development authority (amendment) act, no. 36 of 2007. the lanka rainwater harvesting forum is leading sri lanka's initiative.