Rainwater harvesting

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Rainwater harvesting is the technique of collection and storage of rain into natural reservoirs, tanks, cisterns and other natural and artificial storage units. Rainwater harvesting is also related to the proper management and possible storage of stormwater, which is precipitation from rain and snowmelt events which flows over land (both impervious and pervious surfaces), to advance the infiltration and deceleration of surface water into subsurface aquifers (before it is lost as surface runoff). However, rainwater harvesting differs from stormwater harvesting as the runoff is collected from roofs and building surfaces, rather than creeks, drains, roads or any other land surfaces.^[1][2] The exact definitions and exact difference between the two can vary based on cultural, historical and governmental approaches. A properly designed rainwater harvesting system can collect water from a variety of surfaces — tiles, metal sheets, plastics — and direct the flow to a storage unit to provide the end-user with a potable (of drinkable quality) or non-potable water supply.

Rainwater harvesting is also a component of sustainable water management, whereby the water quality of local stormwater systems is improved and the overall quantity reduced during rain events in order to prevent flooding, erosion and other undesirable consequences.

The construction and use of cisterns to store rainwater can be traced back to the Neolithic Age, when waterproof lime plaster cisterns were built in the floors of houses in village locations of the Levant, a large area in Southwest Asia, south of the Taurus Mountains, bound by the Mediterranean Sea in the west, the Arabian Desert in the south, and Mesopotamia in the east. By the late 4000 BC, cisterns were essential elements of emerging water management techniques used in dry-land farming.^[3]

Studies on rainwater harvesting often focus on sizing of cisterns and tanks and the financial feasibility of installing rainwater harvesting systems. Far more research currently exists on topics that cover residential and domestic installations and systems.

New research on the technical and financial feasibility of rainwater harvesting systems in public buildings has found that "public buildings with small coverage areas can have a good water saving potential, as long as the demand is low and the climatic conditions are favorable to the use of rainwater."^[4]

The typical elements of all rainwater harvesting systems in order of flow are the collection surface, system of conveyance, prefiltration, storage and the delivery system. Depending on the end-use and integration with the overall water plumbing of the building or structure, certain derivations of designs and concepts will cause increased complexity of the system. Another common element integral to potable rainwater harvesting, not necessary in non-potable systems, is the system of post-filtration, treatment and disinfection.

Conventional Rainwater Harvesting Systems		Alternative Rainwater Harvesting Methods
General Rainwater Harvesting System		Fog Harvesting
Small Rainwater Harvesting System	Large Rainwater Harvesting System	Dew Harvesting

In rural areas rainwater harvesting systems answer three questions:

What: Rainwater harvesting will improve the stability and quality of local water supply, contributes to sustainable stormwater management, reduces potable water used for food production and irrigation, and can promote other sustainable development goals.

Who: Decentralized users: From water insecure households or individuals in rural areas, to schools and hospitals in metropolitan areas, all communities can benefit from rainwater harvesting systems.

How: Since rainwater harvesting leads to water supply which leads to food security, this will greatly contribute to income generation.

Salyan and Dailekh, Nepal	Salyan District, Nepal	Kajiado, Kenya - 3R and MUS	Rwambu, Uganda - Clearwater Revival	Rwambu Uganda Hills

3R (Recharge, Retention & Reuse)	Business Development - Micro-financing	Multiple Use Services (MUS)	SamSam RWH Tool
Rain is Gain Tool	Rainwater Harvesting GIS Map	WASH Environmental Sustainability Assessment

The return on investment for rainwater harvesting systems is typically calculated by the investment into the rainwater harvesting system compared against the reduced or avoided cost of municipal water. The cost of avoided or reduced municipal water can also be defined as water savings which would be established against the typical use of water without a rainwater harvesting system.

${\displaystyle Cost{_{R}}{_{W}}{_{H}}\pm Savings{_{M}}{_{W}}=ROI}$

However, more than one variable could be used to calculate the externalized cost benefits that a rainwater harvesting system can provide both for the user and for the community and watershed in which it is placed. For example, the benefit of not having to repair municipal infrastructure due to minimizing average stormwater flow could possibly be written off as tangible savings for a city government. Or quantifying the amount of water that needs to be reduced during heavy rain events to prevent multiple sewage overflows could play a role in calculating the assets a rainwater harvesting system can add.

Rainwater calculators use environmental and system parameters to determine optimum tank sizes.

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The following projects utilize rainwater harvesting techniques, as seen on the Akvo Really Simple Reporting (RSR) pages.

• WASH program in Rural Bangladesh
• Scale up of Sustainable Water Access
• Etude technique d’avant-projet
• Rainwater harvesting for Nicolas School
• Safe water supply for Fayaco, Senegal
• Rainwater Harvesting Capacity Center
• Support on WASH - in Miyo woreda
• Upscaling CLTS for Healthy Communities
• Partnership in WASH services delivery
• Northern Region WASH Programme
• Raising awareness on rainwater harvesting
• Wetland Management & Water Harvesting
• Rain Water Harvesting in Nepal
• Rainwater Harvesting in Kenya
• Rainwater harvesting in Guinee Bissau 2

Here are conversations about rainwater harvesting (RWH) including best practices, troubleshooting, and advice about tanks and systems. Sourced from the Dgroups website, which is a free member-only forum, where people can ask a pool of over 3,000 members about rainwater harvesting. You can always become a member on their site for greater involvement, if you have questions you need to know for your RWH project. Go to the Community Exchange.

• Many of the tools, technologies, and projects on this page are courtesy of the Rainwater Harvesting Implementation Network.
• Original Akvopedia article: akvopedia.org/wiki/Rainwater_Harvesting

Wikimedia Commons has media related to Rainwater harvesting.

Search for Rainwater harvesting on Wikipedia.

• w:Rainwater harvesting
• w:Water conservation
• Portal:Water Technologies

1. ↑ http://www.environment.nsw.gov.au/resources/stormwater/managestormwatera06137.pdf page 10
2. ↑ "Rainwater harvesting 2012". 2012. Archived from the original on 2013-06-06. Retrieved 2012-11-01.
3. ↑ Mays, Larry; Antoniou, George; Angelakis, Andreas (2013). "History of water cisterns: Legacies and lessons". Water 5 (4): 1916–1940. doi:10.3390/w5041916. https://repository.asu.edu/attachments/183018/content/History%20of%20water%20cisterns_2013.pdf. 
4. ↑ Raisa Nicole Campos Cardoso, C. J. C. B., Juliana Maia Duarte. (2020). Technical and financial feasibility of rainwater harvesting systems in public buildings in Amazon, Brazil. Journal of Cleaner Production.