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Rainwater Harvesting Methods; Technology; Advantages

Rainwater Harvesting Methods; Technology; Advantages

Rainwater Harvesting Technologies For Small Scale Agriculture/Gardening


Rainwater harvesting (RWH) is a simple technique by which rainfall is collected for future usage. The collected rainwater may be stored, utilized in dissimilar ways or directly used for recharge purposes. With depleting groundwater levels & fluctuating climate conditions, RWH can go a long method to help mitigate these effects. Capturing the rainwater can help recharge local aquifers, reduce urban flooding & most importantly, ensure water availability in water-scarce zones. While the term seems to have picked up greater visibility in the last few years, it was, & is, even today, a traditional practice followed in rural India. Some ancient rainwater harvesting technique followed in India includes madakas, ahar pynes, surangas, taankas & many more.

This water conservation process can be easily practiced in individual homes, apartments, parks, offices and temples too, across the world. Farmers have revitalized their dry bore wells, created water banks in drought areas, greened their farms, increased the sustainability of their water resources & even created a river. Technical know-how for the rooftop Rainwater harvesting with direct storage can be availed for better implementation. Rainwater harvesting an effective method in water-scarce times, it is also an easily doable practice.

The reasons for using rainwater harvesting systems:

Harvesting rainwater makes sense for a variety of economic & environmental reasons:

Rainwater harvesting will improve water supply, food production, & ultimately food security. Water insecure individuals in rural areas will advantage the most of rainwater harvesting systems. Since rainwater harvesting leads to water provide which leads to food security, this will greatly contribute to income generation.

Rainwater harvesting is a system of collection and storage of rainwater into natural reservoirs or tanks, or the infiltration of surface water into subsurface aquifers (before it is lost as surface runoff). One technique of rainwater harvesting is rooftop harvesting. Other uses include water for gardens, livestock, & irrigation, etc.

  • Rainwater is an economical option for public water, especially for exterior water uses, such as landscape irrigation that need minimal filtration. Although initial equipment installation can be very important, long-term costs are minimal.
  • Rainwater can add limited groundwater resources. With reduced extraction rates, low-yield groundwater wells & springs can last indefinitely. Rainwater can also supplement surface water resources threatened by rapidly rising municipal water use.
  • Rainwater is often the only viable water basis in arid regions or on islands where other water sources may be high in salt, limited in availability, or expensive.
  • Rainwater is low in minerals, so it is ideal for laundry, dishwashing, hair washing, & car washing. Since it contains no chlorine, rainwater is also ideal for filling garden ponds & irrigating sensitive plants.
  • Rainwater harvesting is not regulated by municipal water restrictions. During periods of drought, rainwater can protect investments in landscaping, garden ponds, & swimming pools.
  • Rainwater can cause leaky basements, eroded foundations, overflowing sewers, soil erosion, & water pollution. Collecting rainwater can remove these problems while eliminating the need for expensive stormwater controls.

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Why Rainwater Harvesting?

The rainwater Harvesting method yields copious amounts of water. From an average rainfall of 1,000mm, roughly four million liters of rainwater can be collected in a year in an acre of land (4,047 m2), post-evaporation.

  • As Rainwater harvesting is neither energy-intensive nor labor-intensive, a cost-effective alternative to other water-accruing methods, such as desalination of seawater and water transfer.
  • With the water table falling rapidly, and with concrete buildings, paved car parks, business complexes, & landfill dumps taking the place of water bodies, landfill dumps taking the place of water bodies, Rainwater harvesting is the most dependable solution for augmenting the groundwater level to attain self-sufficiency in public distribution of water.

Example rainwater harvesting in India:

Tamil Nadu is the first Indian state to build rainwater harvesting mandatory. On 30 May 2014, the state government announced that it will set up 50,000 rainwater harvesting structures at different parts of the capital city of Chennai.

Around 4,000 temples in Tamil Nadu state traditionally had water tanks that were used for different rituals. The tanks also served as natural aquifers & helped recharge groundwater. Over the years, though, many of these tanks have gone out of use. Overflowing mounds of silt & garbage have replaced the water in them.

Techniques of Rainwater Harvesting for small scale agriculture:

  1. Rain barrels:

It is the easiest and affordable technique of rainwater harvesting, especially at home. It is where water tanks installed below the downspouts of the rooftop guttering system. The water is then funneled or directed into the tanks. The tank can be connected to give backup water to your current plumbing system, or it can be attached to a pipe for drip irrigation. The use of barrels or tanks is ideal since it can store important amounts of water.

  1. Dry system:

It is related to the barrel’s system, but with the dry system, a larger storage container is used. The container is generally a few meters away from the property. The gutter is redesigned so that water is diverted to the huge storage tank. It is a quick & cheap method to implement but has significant rewards.

  1. Wet System:

It is a method that is entirely different from the dry system. Here, the set pipes will always have water in them. It is because they will be located underground. In the wet method, collection pipes are linked to the downspouts of a building & diverted into a storage tank, which is also underground. The pipes need to be secure & well maintained to ensure there is no leakage into the soil.

  1. Green Roof:

This process of harvesting does not need the use of storage tanks. Instead of storing the water in a reservoir, the water is channeled directly to the garden. The procedure will require installing a drainage system on a building’s roof straight to the backyard. It is a very low maintenance process.

How Rainwater Harvesting solves the water shortage?

Harvesting and collection of rainwater is a proper method that can be used to address the problem of the water crisis in various parts of the world. This water conservation technique can be used to put forward a remarkable solution in areas where there is enough rainfall but not enough supply of groundwater.

Bangalore is a superb example where rainwater harvesting can become very beneficial. Bangalore is an area with a very high population & an area that also has to deal with water shortages. With these in mind, practicing water conservation methods such as rainwater harvesting is a perfect way to ensure an increased supply of water.

Bangalore experiences quite an immense quantity of rainfall almost throughout the year. Therefore, rainwater harvesting will play a huge role in providing additional sources of water. During the dry season, people will be able to have water sources if they had implemented the essential kind of harvesting techniques. With increased demand for water, rainwater collection can be able to assemble the requirements.

When builders & architects are designing a new home or building, it is important that they think of implementing rainwater harvesting methods. It will be able to reduce reliability on other normal resources for groundwater. In the long run, there will be energy savings, water savings, & resource savings.

Rainwater harvesting used for collecting and storing rainwater from rooftops, land surface or catchments using various techniques such as tanks or check dams or recharge to the aquifer. Most promising alternatives for providing fresh water in the face of increasing water scarcity and escalating demand.

Basic Components of RWH:

  • Precipitation
  • Collection of water from the surface catchment
  • Water storage
  • Distribution of water

Rainwater Harvesting – Purposes

Rainwater Harvesting Purpose.
Rainwater Harvesting Purpose.

Rainwater Harvesting employs of a wide range of methods to collect and store rainwater. These methods can be divided into in situ and ex situ types depending on the source of the collected water. In situ rainwater harvesting methods are soil organization strategies that enhance rainfall infiltration and reduce surface runoff, such as planting different plant species. Ex situ systems capture water from areas such as rooftops, land surfaces, steep slopes, road surfaces or rock catchments & store it in storage tanks.

Storage processes for this captured water often are basins behind dams, ponds, tanks or cisterns. Depending on the size of the storage, ex situ systems can be divided into Passive & Active Harvesting systems. Passive harvesting systems (e.g. Rain barrels) are normally small volume systems (50-100 gallons) that capture rooftop run-off without further treatment. Thus, the captured water is generally not used for drinking purposes. Due to their size, passive harvesting systems are generally used in residential applications. Active harvesting methods (e.g. Cisterns) are larger volume systems (typically 1,000 – 100,000 gallons) that capture run-off from roofs or other suitable surfaces such as terraces & road surfaces. Active harvesting systems give water quality treatment and use pumps to supply water to a distribution system. While passive systems are normally used by individual households, active methods can be used on a municipal level, thus benefitting the entire community.

Rainwater Harvesting techniques can provide the following purposes:

Two main purposes: Agricultural & human consumption

  • Freshwater augmentation technology
  • Increase groundwater recharge
  • Reduce storm water discharges, urban floods & overloading of sewage treatment plants
  • Reduce seawater ingress in coastal areas

Methods of Rainwater Harvesting for small scale agriculture:

Roof top rainwater harvesting

This method is the collection & storage of rainwater for reuse on-site, rather than allowing it to run off. These stored waters are used for different purposes such as gardening, irrigation, etc. Different methods of rainwater harvesting are described in this section.

  1. Surface runoff harvesting

In the urban region, rainwater flows away as surface runoff. This runoff could be caught & used for recharging aquifers by adopting appropriate methods.

  1. Rooftop rainwater harvesting

It is a method of catching rainwater where it falls. In rooftop harvesting, the roof becomes the catchments, & the rainwater is collected from the roof of the house or building. It can either be stored in a tank or diverted to an artificial recharge scheme. This technique is less expensive if implemented properly helps in augmenting the ground water level of the area.

Rooftop collection systems for small scale agriculture:

Rooftop collection systems are common, taking advantage of drainage & gutter systems.  Metal roofs are perfect for rainwater collection.  They are easy to keep clean & maintain a high level of rainwater quality.  Some roofing materials, such as asphalt, water uses to non-potable ones.

  1. Conveyance systems via gutters, channels, & pipe systems are used to carry collected water in storage and areas of use.
  2. Storage systems keep together a rainwater for later use. These are normally tanks, either on the surface or below ground. Open ponds may be used, particularly for decorative effect.
  3. Treatment will be required for most potable uses & possible for some non-potable uses. Treatment normally includes filtration to remove particulate matter in the collection & conveyance of the rain water. Simple disinfection (chlorination, ultraviolet – UV, solar) may be necessary to control microbial growth in various systems, including storage systems.
  4. Distribution of water stored to its intended use may require a system of pumps, pipes, & controls.

The system mainly constitutes of following sub components:

  • Catchments
  • Transportation
  • First flush
  • Filter


The surface that receives rainfall straight is the catchment of rainwater harvesting system. It may be terraced, courtyard, paved or unpaved open ground. The terrace may be flat RCC or stone roof or sloping roof. Therefore the catchment is the area, which really contributes rainwater to the harvesting system.


Rainwater from rooftop should be carried during the down, take water pipes or drains to storage or harvesting system. Water pipes should be UV resistant of necessary capacity. Water from sloping roofs could be caught through gutters & down take the pipe. At terraces, the mouth of the each drain should have wire mesh to restrict floating objects.

First Flush:

First flush is a machine used to flush off the water received in the first shower. The first spray of rains needs to be flushed-off to avoid pollute storable or rechargeable water by the probable contaminants of the atmosphere & the catchment roof. It will help in the cleaning of silt & other material leave on the roof during dry seasons Provisions of first rain separator must be made at the outlet of each drainpipe.


There is some skepticism regarding Roof Top Rainwater harvesting since doubts are raised that rain water may contaminate groundwater. There is a remote opportunity of this fear coming true if the proper filter mechanism is not adopted. Secondly, all care must be taken to see that underground sewer drains are not punctured & no leakage is taking place in close vicinity.

Filters are used for the treatment of water to effectively remove turbidity, color & microorganisms. After the first flushing of rainfall, water should pass during filters. A gravel, sand and ‘netlon’ mesh filter are designed & placed on top of the storage tank. This filter is important in keeping the rainwater in the storage tank clean. It removes silt, dust, leaves & other organic matter from entering the storage tank.

The filter media must be cleaned daily after every rainfall event. Clogged filters prevent rainwater from easily entering the storage tank & the filter may overflow. The sand or gravel media should be taken out & washed before it is replaced in the filter.


Due to its several advantages, rainwater harvesting has established increased attention in the last decades and both government and NGOs have started promoting rainwater harvesting as a solution to water scarcity & water access. Therefore, a rapid expansion of rainwater catchment systems has occurred, especially in Asian & African countries facing water scarcity. Rainwater harvesting is mostly a local intervention & a decentralized method of gaining access to clean drinking water. Unlike large-scale water systems such as pipelines or dams which have to be built, financed & managed by governments, rainwater harvesting techniques can be implemented by small communities or even individuals. Active harvesting systems are normally more expensive. The total costs for active systems vary widely depending on the size & complexity of the system. For simple systems, which collect water from roof areas without further water treatment, the storage volume is the major driver of the costs. Depending on the size & material used, the costs are typically between $1.50 – $3.00 per gallon of storage, with per gallon costs generally decreasing with increasing tank size. Additional costs for water treatment and distribution methods often increase the costs by an additional $2.00 – $5.00 per gallon of harvesting system capacity. Consequently, prices for active harvesting systems may range from $1,500 to tens of thousands of dollars, depending on size & complexity. Additionally, maintenance costs of a few hundred dollars per year have to take into account.

Even though rainwater harvesting can be expensive, particularly for small villages & communities in developing countries they are still far more economically feasible than large-scale projects & relatively easy to subsidize by governments. Building dams or a sufficient infrastructure to distribute water across countries can cost many millions of dollars, far more than rising countries could afford.

Small-scale projects like rainwater harvesting method can be funded by multiple sources: governments, communities & non-governmental organizations. In fact, several NGO’s like The Water Project or Charity Water fund rainwater harvesting technologies. However, just the willingness to help does not essentially lead to a successful project.

Hydrological Aspects of rainwater harvesting for small scale agriculture:

  • Hydrology – the study of water although there is plenty of learning about water. Although there is plenty of water on earth, it is not always in the right place, at the right time, & of the right quality.
  • Hydrology – to understand the complex water systems of the Earth & help to solve water problems.
  • Rainfall – a major source of water
  • Hydrological cycle – Change in phase in vary in phase in the hydrosphere
  • Balance of water on Earth remains moderately constant over time

Advantages of the Rainwater Harvesting for small scale agriculture:

  • It provides self-sufficiency for water supply
  • It reduces the cost for pumping of groundwater
  • Provides very high quality water, soft & low in minerals
  • Improves the quality of ground water during dilution when recharged to groundwater
  • It reduces soil erosion in urban areas
  • Rooftop rain water harvesting is very less expensive
  • Rainwater harvesting systems are easy which can be adopted by individuals
  • Rooftop rainwater harvesting systems are easy to construct, operate & maintain.

Disadvantages of the Rainwater Harvesting for small scale agriculture:

The main disadvantage of rainwater harvesting method is the limited supply and uncertainty of rainfall. Rainwater is not a dependable water source in dry periods or in time of prolonged drought. Low storage capacity will limit rainwater harvesting potential, whereas increasing storage capacity will add to construction & operating costs making the method less economically viable. The effectiveness of storage can be partial by the evaporation that occurs between rains.

Read: Soil pH Importance In Agriculture.

Pic Source: Wikipedia.

Last Updated: February 23, 2019
Author: Jagdish


  1. Very informative and enlightening. There was no reference of a small pump in getting the water from storage for use around the house and garden as the pressuer of the water may not be sufficiently heavy. This will be an additional cost to the householder. I live on a very small Caribbean island called Carriacou. and for centuries we have lived and farmed by harvesting rainwater. This water was collected from the roofs by guttering and stored in concrete cisterns and barrels.

  2. Thanks for the sharing this informative article. I love to collect rain water by rain chains. Currently I am looking for this. Can you tell me where I could find it with different types.

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