According to Unesco, population growth, urbanization, industrialization, and increases in production and consumption have all generated ever-increasing demands for freshwater resources. By 2030, the world is projected to face a 40% global water deficit under the business-as-usual climate scenario (2030 WRG, 2009). The fact is there is enough water to meet the world’s growing needs, but not without dramatically changing the way water is used, managed and shared.
Time spent gathering water or seeking safe sanitation accounts for billions in lost economic opportunities. In this regard Rainwater harvesting is one of the most sustainable and economical processes.The process includes the accumulation and deposition of rainwater for reuse on-site, rather than allowing it to run off. Rainwater can be accumulated from rivers or roofs, and in many places, the water collected is redirected to a deep pit (well, shaft, or borehole), a reservoir with percolation, or collected from dew or fog with nets or other tools. Its uses include water for gardens, livestock, irrigation, domestic use with proper treatment, indoor heating for houses, etc. The harvested water can also be used as drinking water, longer-term storage, and for other purposes such as groundwater recharge. Rainwater harvesting is one of the simplest and oldest methods of self-supply of water.
The collection of rainwater is known by many names throughout the world. It ranges from rainwater collection to rainwater harvesting to rainwater catchment. In addition, terms such as roof water collection or rooftop water collection are also used in other countries. We believe that rainwater harvesting is a viable technology in an urban setting. All that is necessary to take advantage of this resource is to capture the free water falling on your roof and direct it to a rainwater storage tank.
The system Advantage:
Rainwater harvesting provides an independent water supply during regional water restrictions, and in developed countries, is often used to supplement the main supply. It provides water when a drought occurs, can help mitigate flooding of low-lying areas, and reduces demand on wells which may enable groundwater levels to be sustained. It also helps in the availability of potable water, as rainwater is substantially free of salinity and other salts. Application of rainwater harvesting in urban water system provides a substantial benefit for both water supply and wastewater subsystems by reducing the need for clean water in water distribution system, less generated stormwater in the sewer system, and a reduction in stormwater runoff polluting freshwater bodies. Many countries, especially those with arid environments, use rainwater harvesting as a cheap and reliable source of clean water. To enhance irrigation in arid environments, ridges of soil are constructed to trap and prevent rainwater from running down hills and slopes. Even in periods of low rainfall, enough water is collected for crops to grow. Water can be collected from roofs, and dams and ponds can be constructed to hold large quantities of rainwater so that even on days when little to no rainfall occurs, enough is available to irrigate crops.
In both urban and rural setting, harvesting can be done by the use of infrastructure. One of the simplest ways of storing water from the collection is storage tanks. In most cases, the harvested water is usually redirected to storage tanks, cistern or reservoirs. The water is usually stored for later use. The roof of buildings is the best way to harvest rainwater. There are numerous advantages in doing so.
1. Easy Preservation: The use of rainwater harvesting system provides ideal merits to any community. First and foremost, the collection offers a better and efficient utilisation of energy resource. It is important because potable water is usually not renewable, thus reducing wastage. The systems used for water collection is based on simple techniques that are very easy to maintain. The overall expenses used in setting up harvesting methods are much cheaper compared to other purifying or pumping means. Also, its maintenance is feasible on the economic front as it does not require deep pockets.
2. Utility Management: Water that has been stored from harvesting water can be used for several non-drinking purposes. It will immediately reduce one’s utility bills. It is ideal for both residential and commercial properties. Even a small rainwater harvesting system can result in decreased quarterly water bills. Rainwater harvesting systems are especially beneficial in large buildings, or buildings with high water demand and large roofs, such as schools, farms and leisure centres.
3. Facilitating Irrigation: Harvesting allows the collection of large amounts of water. Most rooftops provide the necessary platform for collecting water. Rainwater is usually free from harmful chemicals, which makes it ideal for irrigation purposes.
4. Less dependency: Another important advantage is that it reduces demand for potable water. It is important especially in areas with low water levels.
5. Storm Water Retention: Another great benefit is that the system help with stormwater retention and attenuation. This is especially important within an urban landscape, where water that can be captured and held on site will significantly reduce the volume of water discharged to the main drainage system, thus reducing flood risk.
6. Environmentally Friendly: Rainwater harvesting systems are energy efficient and environmentally friendly, requiring no chemicals for water treatment. Treatment is done by filtration, as will be explained later in this document.
7. Compiling with BREEAM Requirements: Some commercial building projects have to comply with a sustainability assessment method known as BREEAM (Building Research Establishment Environmental Assessment Method). Reducing the use of water within a building will earn credits that count towards the BREEAM score.This will depend on what level of BREEAM is to be achieved.
Rainwater harvesting is not a new phenomenon, but until recently the technologies have not been widely available to conserve, clean and distribute water efficiently enough to make it a viable option in domestic properties. However, thanks to a new generation of innovative rainwater harvesting solutions, these options are now available at an affordable rate to homeowners. Rainwater harvesting systems are especially cost-effective when incorporated into a pro-perty development at the design stage. Discussed below are some its important types.
Submersible: In this process, the pump is located within the underground tank and harvested water is simply pumped directly to the WC or other appliances. If the tank should be in danger of running dry, a small amount of mains water is fed to it in order to maintain supply. For commercial projects, such systems tend to be dual pump arrangements..
Suction: This system differs in that the pump is not inside the tank, but instead is located within a control unit within the house (e.g. utility room).
Manual System of gravity push: This type of system differs in that the harvested water is first pumped to a high-level tank (header tank), then allowed to supply the outlets by gravity alone. With this arrangement, the pump only has to work when the header tank needs filling. Also, the mains water is fed directly to the header tank, not into the main harvesting tank.
Indirect Pumped: This arrangement is similar to the above, except that the internal tank can be at any level in the building, as it does not rely on gravity to supply the outlets. Instead, a booster pump set is used to provide a pressurized supply. This system employs the benefit of not having to feed mains back-up water to the underground tank, whilst also offering great flexibility as the booster pumps can be tailored to suit the flow and pressure requirements of the building.
Water Butt: In this process, Water collects in the container from drain pipes and/or natural rainfall, and is mainly used for the watering of garden plants. Users with gardens of a decent size will see a reduction in the amount of mains water used. Pairing the water tank with a rainwater filter can further improve the quality of the harvested rainwater.
Gravity Only: In some situations It may be possible to have a system that functions purely through gravity, requiring no pump and therefore no energy use. With this arrangement, rainwater is collected from a part of the roof which has gutters above the filter and collection tank which are in turn above all the outlets. This arrangement is ONLY ever possible where the storage tank can be located below the level of the gutters, yet higher than the outlets that it will supply. Only the power of gravity is needed to feed collected and filtered water to various parts of the home for use, so it is an ultra-energy efficient option.
Techniques for rainwater harvesting:
Rain Barrel Installation: The simplest way to harvest rain is through a rain barrel linked to a pipe fitted to collect rainwater from the rooftop and verandah of the house. To prevent the barrel from becoming a mosquito breeding ground, fasten a tight-fitting top to it, and screen the ends of the downspouts leading into the barrels. It coats the water’s surface and kills larvae by depriving them of oxygen.
Dry System: The dry system of rainwater harvesting is essentially the barrel system scaled up in size. A larger container is placed next to the property, offering a larger storage capacity than a barrel, and the guttering is diverted to the top of the tank. Like the barrel method, it is reasonably cheap and easy to implement. It gets the name ‘dry’ because essentially the collection pipe ‘dries’ after each rain event since it empties into the top of the tank. This makes it a good choice for plots in areas prone to infrequent but large storm events.
Wet System: The wet system refers to the collection pipes being constantly full of water. This is because they are underground. Multiple collection pipes are fitted to several downspouts on the property and then run underground to the storage tank. The rainwater will rise through the pipes and spill into the tank. When it is not raining the level remains static and the pipes full. Because of the constant presence of water in the pipes, it is essential that they are watertight to prevent leakage into the soil. It is more expensive to install that the barrel or dry system, due to the underground piping, but does have the benefit that you can locate the tank anywhere on the property.
Creation of Green Roof: This method does not need the use of storage tanks. Instead of storing the water in a reservoir, the water is channeled straight to the garden. The process will require installing a drainage system on a building’s roof straight to the backyard. It is a very low maintenance method.
Rain Garden System: In this process, one uses native plants, local soil, and mulch to remove pollutants from water, and allows it to percolate into the ground. It’s easy to create and is quite sustainable.
Surface runoff harvesting: In an urban area, rainwater flows away as surface runoff. This runoff could be caught and used for recharging aquifers by adopting appropriate methods.
Rooftop rainwater harvesting: It is a system of catching rainwater where it falls. In rooftop harvesting, the roof becomes the catchments, and the rainwater is collected from the roof of the house/building. It can either be stored in a tank or diverted to artificial recharge system. This method is less expensive and very effective and if implemented properly helps in increasing the groundwater level of the area.
Rain Chains: The environment-friendly accessories used in the creation of rain chain help avoid the runoff by transporting rainwater from the collecting pipe downwards to a drain or to a storage container.
Splash Back System: Splash block is a piece of concrete or plastic of a roughly rectangular shape and is placed below the downspout that carries rainwater from the roof of a house during rainfall. It absorbs the force of the water that is getting diverted from the roof and also prevents holes from being dug in the garden.
Rain saucer: The rainsaucer unfolds to form a funnel which fills the containers with rainwater. This system also decreases the chances of contamination.
Government plans to make 23 lakh rain water harvesting structure
Tamil Nadu was the first Indian state to make rainwater harvesting mandatory. On 30 May 2014, the state government announced that it will set up 50,000 rainwater harvesting structures at various parts of the capital city of Chennai. Following sustained campaigns by voluntary organisations and departments in charge of water distribution and use, authorities in Chennai too decided to restore around 40 major temple tanks in the city. The aim is to convert the tanks into catchments for rainwater harvesting.
In freshly announced news it is reported that the government is working on a master plan envisaging construction of about 23 lakh artificial recharge and rainwater harvesting structure in rural areas and 88 lakh in urban areas. According to economic times reports, Minister for Drinking Water and Sanitation Narendra Singh Tomar said the Central Groundwater Board has prepared a conceptual document entitled ‘Master Plan for Artificial Recharge to Groundwater in India’ involving ground water scientists and experts. “The master plan envisages construction of about 23 lakh artificial recharge and rain water harvesting structure in rural areas and 88 lakh rain water harvesting structures in urban areas,” he exclaimed.
Harvesting and collection of rainwater is a proper way that can be used to address the problem of the water crisis in various parts of the world. This simple water conservation method can be used to put fo ward a remarkable solution in areas where there is enough rainfall but not enough supply of groundwater. According to Times Of India Report, Water scarcity is fast becoming urban India’s number one woe, with government’s own data revealing that residents in 22 out of 32 major cities have to deal with daily shortages. The worst-hit city is Jamshedpur, where the gap between demand and supply is a yawning 70%. The crisis is acute in Kanpur, Asansol, Dhanbad, Meerut, Faridabad, Visakhapatnam, Madurai, and Hyderabad – where supply fails to meet almost 30% of the demand.
According to qz.com, India now uses more groundwater than China and the United States combined. At present India uses 230-250 cubic kilometers of groundwater each year. This accounts for about one-quarter of the global groundwater use. More than 60% of irrigated agriculture and 85% of domestic water use now depends on groundwater. India now uses more groundwater than China and the United States combined.
Bangalore and Delhi is an excellent ex-ample where rainwater harvesting can be-come very beneficial. With these in mind, practicing conservation methods such as rainwater harvesting is an ideal way to en-sure an increased supply of water. When builders and project managers are evaluating a new design for a building, it is important that they think of sing g rainwater harvesting methods to its potential. It will aid in the reduction of reliability on other natural resources in the long run which will ultimately lead to energy savings, water savings, and resource savings.