Sustainable rainwater harvesting and the water crisis in KathmanduRainwater harvesting, along with permeable pavement co-management, can help realise both anthropogenic and environmental benefits.
In some of the more arid areas of the United States, rainwater harvesting is regulated by the state government because of concerns that excessive rainwater sequestration by landowners can keep the water from entering its natural watershed—causing huge environmental and social damage downstream. Perhaps one of the more dramatic cases happened in 2012, when an Oregon man sequestered enough rainwater to fill 20 Olympic-sized swimming pool—effectively depriving this water to the rest of the ecosystem. In response, the Oregon government drained the water and jailed and fined the man. To prevent issues like these, different US states have different laws regarding the quantity of rainwater that homeowners can harvest. These laws vary widely with some having a zero-tolerance policy for any scale of such rainwater systems.
While these regulations were made to help protect the environment, in their more extreme forms, they may do more damage than good. There is plenty of science that dictates that sustainable rainwater harvesting can reduce our environmental impact by decreasing our dependence on groundwater and reducing energy and infrastructure requirements for transporting water over long distances.
Rainwater harvesting is a good solution to the water crisis that many parts of Kathmandu Valley face today. Harvesting systems—that also have in-built mechanisms to store water for future use and recharge groundwater—can help us divest our dependence on unreliable tap, and expensive tanker, water.
Suman Shakya, the co-founder of Smart Paani, describes himself as water independent, ‘For six months a year, my household runs easily on rainwater’, he says. ‘In fact, there is even a surplus of rainwater that overflows into a shallow well—that I rely on for the rest of the year. And the water that comes out of my tap is so clean that I can drink straight out of it’, adds Shakya. What makes this independence possible is the extensive rainwater capture and chemical-free filtration and storage system that has been built into his house.
Kathmandu’s air is polluted. So, many people believe that rainwater is not potable as it mixes with these airborne contaminants. While rain does wash down a lot of atmospheric pollutants, it does so within the first few minutes. To ensure that these contaminants are not introduced into the water system, most rainwater harvesting infrastructure are designed to flush out the initial flow before the collection process starts.
Additionally, filters are used to further enhance water quality. For example, Shakya’s home has two different filtration systems in place. One of these, the rapid sand filter, removes large debris before the water flows to underground tanks or groundwater. As the water passes through the filtration system, it also has the opportunity to deoxygenate. This kills bacteria and also prevents the formation of iron precipitates in groundwater that tends to clog aquifers, reducing their capacity to recharge. Another filter, known as the biosand filter, is placed between the groundwater and the tank on top of the roof to ensure that iron, along with heavy metals and bacteria are removed. Depending on the groundwater quality of any site, each household filtration system is optimised to not only increase the purity of the water that enters the house but also to reduce any contaminants that may enter the groundwater system.
Despite the availability of such sustainable technology to generate clean, potable water, rainwater harvesting has yet to be adopted widely by Kathmanduites. One of the biggest deterrents is the initial cost of investment required to put this system in place. However, these investments are usually recovered within the first couple of years once reliance on tankers, boring and tap water decreases. Maintenance of such systems, which entails the removal of filtered particles from the tank, is also a fairly low-key process that homeowners can perform by themselves.
People are also sceptical of how useful such rainwater systems will be in drier months. However, these systems are very efficient in capturing rainwater. A lot of the times, like in Shakya’s case, these systems not only produce water for immediate use but also enough to recharge groundwater—which can later be utilised during dry months. Depending on the size of the rainwater capture area and the household size, this technology can help meet most, if not all, of the water demands within a household.
To ensure sustainability, however, it is important that co-management of permeable pavements take place simultaneously as well. ‘If water is unable to penetrate the ground then it will not be able to replenish groundwater effectively, which has an adverse impact on the long term viability of such systems’, says Shakya. One way to prevent this is by ensuring that natural surfaces are retained wherever possible. ‘If a surface needs to be paved, interlocking bricks (that allow water to permeate through their middle) can be used as an alternative to cement, wherever possible’, comments Shakya. Today, stormwater that should enter shallow aquifers often ends up accumulating on the streets—eventually entering sewer systems. This wasted water not only causes urban flooding but also overwhelms wastewater treatment plants, which causes a lot of infrastructure dysfunction in the city.
As the climate changes, it will affect the Valley’s tap water supply and increase pressure on groundwater. Rainfall patterns will also likely become more erratic, with larger amounts of rainfall being dumped in shorter periods of time. Additionally, population increase will exacerbate water scarcity. In this scenario, to ensure current and future water access to Kathmandu’s population, policies need to be tailored to encourage diversification of water sources, and safe water storage technologies. Sustainable rainwater harvesting will not only help realise these anthropogenic goals, but environmental ones as well.
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