Rainwater Harvesting

Rainwater harvesting (RWH) is a basic technique for collecting rainwater for later use. The rainwater collected can be stored, used in a variety of ways, or used directly for recharge. RWH can go a long way to alleviate the effects of diminishing groundwater levels and changing climate conditions. Capturing rainfall can aid in the replenishment of local aquifers, the reduction of urban flooding, and, most critically, the availability of water in water-scarce areas.

Individual homes, flats, parks, offices, and temples all across the world can simply implement this water saving strategy. Farmers have refilled empty borewells, built water banks in drought-stricken areas, greened their farms, boosted the sustainability of their water resources, and even built a river. 

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Rainwater Harvesting Project

To combat groundwater depletion, the state of Tamil Nadu was the first to make rainwater collection mandatory for all buildings. The project began in 2001 and has since expanded to include all of Tamil Nadu's rural districts. Rainwater harvesting is promoted via posters throughout Tamil Nadu, particularly in rural regions.

Importance of Rainwater Harvesting

Rainwater collection is beneficial in a variety of ways. The most important benefit is that it will alleviate water scarcity while also producing high-quality water if collected and stored properly. Installing a rainwater collecting system can drastically reduce the amount of water used from the mains. It has the ability to prevent droughts in the future. The collection surface, gutters, downspouts, pre-filtration or first-flush devices, storage tanks, and distribution systems which can include purification are all part of the system (depending on the reason you will be using the rainwater for).

Rainwater Harvesting Methods

Different methods of water harvesting are as follows:

1. Surface Runoff Harvesting:

Surface runoff rainwater harvesting is a method of collecting rainwater flowing down the ground during rainstorms and storing it in a tank beneath the ground surface for irrigation and other uses. It is critical to employ efficient and effective water conservation strategies, such as limiting evaporation, while storing rainwater. It is a simple way to learn technology that may be quite profitable if applied correctly. The primary goal of surface runoff rainwater harvesting is to meet the ever-increasing demand for water while also reducing pollution, soil erosion, and road floods.

Rainwater is collected in a tiny confined area such as pits, wells, trenches, shafts, and other similar structures and absorbed beneath the soil through them in this approach. There is no direct benefit from this form of rainwater harvesting because it is an indirect method, but it is the best method for making enough water available under the ground in the long run. Recharging ground water aquifers is another name for this rainwater collection process.

The goal of surface runoff water harvesting is to remove impurities from the water so that it can be reused. To improve storage capacity, small reservoirs with earthen bunds or embankments to limit runoff or river flow are formed from dirt excavated from within the reservoir, and a spillway or weir provides controlled overflow when storage capacity is surpassed.

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2. Rooftop Rainwater Harvesting:

Rooftop rainwater harvesting is a method for collecting rainwater from roof catchments and storing it in reservoirs. Rainwater can be collected and stored in a subsurface groundwater reservoir using artificial recharge techniques to suit household demands. Rooftop rainwater harvesting's main goal is to store water for later use. In dryland, hilly, urban, and coastal environments, capturing and storing rainwater for use is extremely crucial. It's a rainwater collection system that collects rainwater as it falls. The roof of the house/building becomes the catchment in rooftop harvesting, and rainwater is collected from the roof.

It can be stored in a tank or routed to a recharging system. This method is less expensive and quite effective, and it aids in supplementing the area's groundwater level when properly done.

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Components of the Rooftop Rainwater Harvesting:

1. Catchment

The catchment of a rainwater collecting system is the area that directly absorbs rainfall. It could be a terrace, a courtyard, or open ground, whether paved or unpaved. A flat RCC/stone roof or a sloping roof can be used to construct the terrace. As a result, the catchment is the area that contributes rainwater to the rainwater harvesting system.

2. Transportation

Rainwater should be brought down to the storage/harvesting system via water pipes or drains from the roof. UV-resistant water pipes (ISI HDPE/PVC pipes) with sufficient capacity should be used. Water from sloping rooftops could be collected in gutters and piped down. To prevent floating material on terraces, wire mesh should be installed at the drain's mouth.

3. First flush

The first flush is a mechanism that is used to drain the water from the first shower. To avoid contaminating storable/rechargeable water with pollutants from the atmosphere and the catchment roof, the first shower of rain should be rinsed off.

During dry seasons, it will also assist with the removal of silt and other debris from the roof. At the exit of each drainpipe, provisions for the first rain separators should be made.

4. Filter

Rooftop rainfall harvesting is always met with suspicion, as concerns about rainwater contaminating groundwater have been voiced. If the right filter mechanism is not used, there is a remote chance that this worry will come true. Second, extreme caution must be exercised to ensure that subterranean sewer drains are not pierced and that no leaking occurs near them. To successfully remove turbidity, color, and germs from water, filters are utilized. Water should pass through filters after the initial flushing of rainfall.

Following each rainstorm event, the filter media should be cleaned. Filters that are clogged make it difficult for rainwater to enter the storage tank, and they may overflow. Before reinstalling the sand or gravel media in the filter, it should be removed and rinsed.

Advantages of Rainwater Harvesting

In developed countries, rainwater collection provides an independent water source in the face of regional water scarcity, and it is routinely used to supplement the primary supply. It provides water during droughts, can help with flood mitigation in low-lying areas, and reduces well demand, allowing groundwater levels to be maintained. Rainwater is low in salinity and other salts; therefore, it helps to increase the supply of drinkable water. Rainwater harvesting in urban water systems benefits both the water supply and wastewater subsystems by lowering the demand for clean water in water distribution systems, creating less stormwater in sewage systems, and reducing stormwater runoff that pollutes freshwater bodies.

Process of Rainwater Harvesting

Rainwater harvesting procedures are mentioned below:

Independent Water Supply

During periods of water scarcity, rainwater collection provides a reliable source of water. Rainwater harvesting is a crucial source of clean water in locations where clean water is expensive or difficult to get by. Rainwater collecting is commonly done in industrialized countries as a secondary source of water rather than as the primary source, although it can also reduce a household's water expenses or usage levels. Rainwater can be consumed safely if extra treatments are performed prior to consumption. Germs are killed by boiling water. A frequent approach to avoid impurities in the water is to add another supplement to the system, such as a first flush diverter.

Supplemental in Drought

Rainwater collected in previous months can be utilized if a drought occurs. When rain is scarce but unpredictable, capturing the rain that does fall with a rainwater collection system could be critical. Rainwater collection is a cheap and reliable source of clean water in many nations with arid settings. In arid climates, soil ridges are built to collect and keep rainwater from going downhills, so improving irrigation. Even during dry spells, enough water is gathered to keep crops growing. Roofs can be used to collect rainwater, and big rainwater tanks can be built.

Life-Cycle Assessment

A life-cycle assessment is a method for evaluating a system's environmental implications from conception to disposal. Devkota et al. created a rainwater harvesting methodology and discovered that the building design (e.g., dimensions) and function (e.g., educational, residential, etc.) play key roles in the system's environmental performance.

A new metric, the demand to supply ratio (D/S), was established to address the functional aspects of rainwater harvesting systems, finding the appropriate building design (supply) and function (demand) in terms of the environmental performance of rainwater harvesting for toilet flushing. The reductions in environmental emissions were higher if the buildings were connected to a combined sewage network rather than a separate one, based on the notion that rainwater supply saves not only potable water but also stormwater entering the combined sewer network (thereby requiring treatment).

Cost-effectiveness

Although basic RWH systems can supply a source of water to impoverished developing nations, the average cost of an RWH setup varies depending on the technology used. Governmental aid and non-governmental organizations (NGOs) can help impoverished communities by providing the resources and education needed to establish and maintain RWH systems. According to some studies, rainwater collection is a cost-effective and environment-friendly option for water scarcity and other numerous uses. Building new large-scale, centralized water delivery systems, such as dams, has the potential to harm local ecosystems, incur external societal costs, and have limited applications, particularly in developing countries or underprivileged populations. 

Did You Know?

Even if it doesn’t  rain much, You can get a lot of water.

When collecting rainwater, you may collect 600 gallons of water for every inch of rain that falls on a 1,000 square foot roof.

With 10 inches of rain, you could gather 6,000 gallons of water if you built a rainwater harvesting tank under the gutter of that 1,000 square foot roof! That's a lot of water!

When I evaluate people's homes for rainwater collection, I frequently discover that the limiting factor is not the amount of rain we get, but rather the amount of space available for a rainwater tank. Most people's yards aren't big enough for a 6,000-gallon tank!