As the world faces an increasingly critical need to address climate change, the impact that water conservation has on a sustainable environment is undeniable. Groundwater is the primary source of freshwater that caters to the demand of ever-growing domestic, agrarian and industrial sectors of the country. With rapid climatic changes, increase in global temperature and population growth, there is a scarcity of potable water in many countries across the world. The gradual falling of water levels is a cause of serious concern not only because it leads to shortage of usable water but also causes imbalance in salinity in coastal areas. Rainwater harvesting helps manage stormwater runoff to prevent erosion, flooding, and poor water quality in our lakes and streams; thereby reducing flooding, erosion, and groundwater contamination. Another aim of rainwater harvesting is to construct primary resources of land and water to generate secondary sources. For example, during the summer season in India, it helps to provide water to places such as Rajasthan that face a scarcity of water.

This is why water conservation has become very critical.

What is rainwater harvesting?

Rainwater harvesting is the storing of rainwater during the monsoon season for the purpose of using it during periods of water scarcity.

Generally speaking, it is a process used for collecting and storing rainwater for human use. Rainwater harvesting is best described as the technique by which rain water is accumulated into natural reservoirs or tanks or the infiltration of surface water into subsurface aquifers (before it is lost as surface runoff). It is then stored with the intention of reusing it during the dry season or when there is a drought.

The importance of rainwater harvesting lies in the fact that it can be stored for future use. Just as it can be used directly so also the stored water can be utilized to revitalize the ground level water and improve its quality. This also helps to raise the level of ground water which then can be easily accessible.

source: Rainwater-harvesting.webp

How do we harvest rainwater?

Traditionally, this involves harvesting the rain from a roof. The rain will collect in gutters that channel the water into downspouts and then into some sort of storage vessel. The two major types of rainwater harvesting include roof based and land-based rainwater harvesting.

Rainwater harvesting systems consists of the following components:

• Catchment- Used to collect and store the captured rainwater
• Conveyance system – It is used to transport the harvested water from the catchment to the recharge zone
• Flush- It is used to flush out the first spell of rain
• Filter – Used for filtering the collected rainwater and removing pollutants
• Tanks and the recharge structures: Used to store the filtered water which is ready to use

The process of rainwater harvesting involves the collection and the storage of rainwater with the help of artificially designed systems that run off naturally or from man-made catchment areas like- the rooftop, compounds, rock surface, hill slopes, artificially repaired impervious or semi-pervious land surface.

Several factors play a vital role in the amount of water harvested. Some of these factors are:

• The quantum of runoff
• Features of the catchments
• Impact on the environment
• Availability of the technology
• The capacity of the storage tanks
• Types of the roof, its slope and its materials
• The frequency, quantity and the quality of the rainfall
• The speed and ease with which the rainwater penetrates through the subsoil to recharge the groundwater

The collected rainwater may be stored, utilised in different ways or directly used for recharge purposes. With depleting groundwater levels and fluctuating climate conditions, RWH can go a long way to help mitigate these effects. Capturing the rainwater can help recharge local aquifers, reduce urban flooding and most importantly ensure water availability in water-scarce zones.

Techniques of rainwater harvesting

There are two major techniques of rainwater harvesting:

1. Surface runoff harvesting In this method, rainwater flows away as surface runoff and can be stored for future use. Surface water can be stored by diverting the flow of small creeks and streams into reservoirs on the surface or underground. It can provide water for farming, for cattle and also for general domestic use. Surface runoff harvesting is most suitable in urban areas. Rooftop rainwater/storm runoff can be harvested in urban areas through:

• Recharge Pit
• Recharge Trench
• Tubewell
• Recharge Well

2. Groundwater recharge Groundwater recharge is a hydrologic process where water moves downward from surface water to groundwater. Recharge is the primary method through which water enters an aquifer. The aquifer also serves as a distribution system. The surplus rainwater can then be used to recharge groundwater aquifer through artificial recharge techniques. Rainwater in rural areas can be harvested through:

• Gully Plug
• Contour Bund
• Dugwell Recharge
• Percolation Tank
• Check Dam/Cement Plug/Nala Bund
• Recharge Shaft

source: Techniques of rainwater harvesting.webp

Although rainwater harvesting measure is deemed to be a desirable concept since the last few years, it is rarely being implemented in rural India. Different regions of the country practiced a variety of rainwater harvesting and artificial recharge methods. Some ancient rainwater harvesting methods followed in India which includes Madakas, Ahar Pynes, Surangas, Taankas, etc.

Advantages of Rainwater Harvesting

There are multiple benefits of the rainwater harvesting system:

• Helps in reducing the water bill over time
• Decreases the demand for water
• Reduces the need for imported water
• Promotes both water and energy conservation
• Improves the quality and quantity of groundwater
• Does not require a filtration system for landscape irrigation
• The technology is relatively simple, easy to install and operate
• It reduces soil erosion, stormwater runoff, flooding, and pollution of surface water with fertilizers, pesticides, metals and other sediments
• It is an excellent source of water for landscape irrigation with no chemicals, dissolved salts and free from all minerals

In addition to the great advantages, the rainwater harvesting system has a few barriers like unpredictable rainfall, unavailability of the proper storage system, etc.

• Regular maintenance is required
• Requires some technical skills for installation (although, now there are a few startups like Neerain that enable you to install a rainwater harvesting system without any technical knowledge)
• Limited and no rainfall can limit the supply of rainwater
• If not installed correctly, it may attract mosquitoes and other waterborne diseases
• One of the significant drawbacks of the rainwater harvesting system is storage limits

History of rainwater harvesting

• Rainwater has been harvested in India since antiquity, with our ancestors perfecting the art of water management.
• Around the third century BC, the farming communities in Balochistan (now located in Pakistan, Afghanistan and Iran), and Kutch, India used rainwater harvesting for irrigation
• In ancient Tamil Nadu, rainwater harvesting was done in the Chola kingdom.
• Rainwater from the Brihadeeswara temple (located in Balaganapathy Nagar, Thanjavur) was collected in Shivaganga tank.

Some examples of traditional water harvesting system in India

• Zing - Tanks for collecting water from melted ice in Ladakh
• Kul - Water channels in mountain areas of Jammu, Himachal Pradesh.
• Naula -Small ponds in Uttaranchal
• Apatani system - Terraced plots connected by inlet and outlet channels in Arunachal Pradesh
• Zabo - Impounding runoff in Nagaland
• Bamboo drip irrigation - Water from streams in the hills is brought to the plains via bamboo pipes for drip irrigation in Meghalaya
• Dongs - Ponds in Assam
• Dungs or Jampois - Small irrigation channels linking rice fields to streams in the Jalpaiguri district of West Bengal
• Dighis - Small square or circular reservoir fed by canals from rivers in Delhi
• Baolis - Secular structured stepwells from which everyone could draw water and use for washing and bathing
• Baoris / Bers - Community wells in Rajasthan
• Tankas - Underground tank Bikaner in Rajasthan
• Kund - A circular underground well; having a saucer-shaped catchment area that gently slopes towards the center where the well is situated
• Johads - Earthen check dams in Alwar district, Rajasthan