The sky giveth

17 min read
26 May 2017
17 min read
2209 words
If more Kathmanduites took up rainwater harvesting, they would be both able to meet their water needs and help alleviate the city's water woes

The ongoing digging of roads all over the Capital for the laying down of Melamchi's water pipes has turned the city into a dust bowl. Occasionally, the haze that envelops Kathmandu settles when drizzles and downpours tamp down the dust. Melamchi's water might finally be here to put an end to the woes of this dry city, but for decades Kathmanduites have had to suffer acute water shortage problems--even though some of those problems could have been alleviated if the people had turned to rain showers as a water source.  

Until some 30 years ago, the shortage in Kathmandu was not as dire. The piped water systems, in combination with the many dhunge dharas in various toles, could meet the needs of the Valley's denizens. Then, from the 90s, as the population of the Valley began to increase at an alarming rate, the water supply could not keep up with demand. According to The Status of Domestic Water Demand: Supply Deficit in the Kathmandu Valley, a report published in the Multidisciplinary Digital Publishing Institute (MDPI) by Nepali engineers in 2016, there was an estimated supply deficit of 102 million litres per day in Kathmandu Valley last year. And the demand of water is 360 million litres every day, but the supply is only 160 million litres, which decreases to 90 million litres during dry seasons.

Owing to that scarcity, people have had no other choice than to turn to alternative sources like wells and water tanks. But, according to some estimates, 50 billion litres of underground water (which feeds the wells and water tanks) has not been recharged in Kathmandu. Furthermore, owing to the high levels of arsenic, ammonia, iron, nitrates and E coli in the water, the quality of water does not meet the recommended World Health Organization (WHO) guidelines. The other obvious alternative the people of Kathmandu turn to are water tankers that supply 17-20 million litres of water every day, even during the monsoon. In all this, one water source that seemingly everybody overlooks is rainwater. According to the Department of Hydrology and Meteorology, Kathmandu Valley witnesses approximately 1,450-1,600 mm rainfall annually. Despite the volume of rainfall Kathmandu witnesses, and the acute shortage of ground water, only a small number of people actively practice rainwater harvesting.

Simply put, rainwater harvesting comprises the collection and use of rainwater. There are three components that come into play when you harvest rainwater: catchment, conveyance and collection/storage. When the rain falls on your roofs, the roofs act as your catchment area. The water collected on the roofs is then channelled through conveyance pipes (the process is also known as guttering). The first 10 minutes or so of the water that flows is flushed out by a filtering device (known as First Flush Device) because the water contains debris and dust particles present on the roofs. The remaining water is then collected in a filtering tank. Here, the water is strained through either a charcoal water filter, sand filter or screen filter. Then it is pumped into a reservoir. Each square metre of roof should produce one litre of drinkable rainwater that can be harvested. But in practice, you can only harvest 85 per cent of drinkable water. The other 15 per cent, which is filtered out as first flush, can however be used for watering your garden, washing your car, doing your laundry and so on.

In Kathmandu Valley, more than 36,000 litres of rainwater can be effectively collected from a house built on a plot of one aana (with a roof size of around 340 sqft). The bigger the roof size, the more amount of rainwater that can be collected, obviously. Let's suppose you have a 1,000 sq ft catchment area on your roof. With that, you can collect at least 150,000 litres of water throughout the year. Out of this, you'll usually use 15 per cent for drinking. The rest of the water will go into washing, cleaning, bathing, flushing the toilets, and other purposes. In Nepal, approximately 100 litres of water is used by a person every day. So if you are a family of four, you will use around 146,000 litres of water per year.

"Water is the most basic of all necessities, and often the most neglected," says Suman Shakya, managing director of Smart Paani, a company that produces water-harvesting systems. If you look at the weather data, you will see that Kathmandu sees rainfall for almost six to seven months a year--which should be enough to see you through the whole year, if you manage your harvest properly. Of course, the size of your storage tank matters too; this can be a cause of concern for old houses that have small tanks, but if you allow the water to seep into the ground in your compound, then the underground water sources in your area will be recharged--giving you enough water that you can draw through tube wells and so on."

Types of rainwater harvesting systems

Besides setting up rainwater harvesting systems in individual homes, Smart Paani also works with hotels, restaurants, schools and other organisations in Kathmandu, Pokhara, Salyan and Dharan. Smart Paani uses two types of systems to filter rainwater: Rapid Sand Filter and Rainy Filter. In the Rapid Sand Filter setup, the rainwater flows from catchment areas into the gutters. The first flush filtering takes place in the pipes, after which water is then transferred into a tank--which is a customised sand filter consisting of layers of sand and gravel, which remove the remaining dirt and reduce the bacteria in the water. Their Rainy Filter is a more basic setup that uses a screen to filter the water. The Rainy Filter system includes a self-cleaning mechanism and the system can be fixed to a wall by connecting it to your house's rainwater drain pipes. In the Rainy Filter setup, the water enters through an inlet, rotates slowly in an angular motion that creates a centrifugal force, which helps separate the dirt particles from the clean water.

Best Paani, another company based in Kathmandu, focuses on installing rainwater-harvesting systems in schools all over Nepal, in collaboration with local government bodies, financial institutions and donors. "We focus on schools, rather than just houses, because the impact we can make in high-density areas such as schools and hospitals is far greater than that in houses," says Sajal Pradhan, managing director of Best Paani.

Best Paani's systems include Rain Water Collection, Water Filtration (non-electric and non-chemical) and Ground Water Recharge (by directed surplus rain water) units. The company uses 100 per cent locally available materials, including ISO verified PVC, sand and metal gutter brackets.

You can use harvesting systems created by companies, but if you are good with tools, you can build it by yourself too. Tara Puri, a civil engineer by profession, designed and set up his own rainwater harvesting system at his house in Balaju. "My house does not get even a drop of water from the city mains. To solve the perennial water shortage in my home, I set up my own rainwater harvesting system. I figured out that I could use the monsoons to solve my problem," says Puri. Puri has turned three of his terraces into catchment areas for collecting rainwater. The collected water gets channelled through conveyance pipes into two 750 litre tanks (after going through first flush filters). The water then goes to the underground reservoir, from where it is pumped to the house's overhead tank. For drinking purposes, Puri processes the water in an electric purifier. "If it rains heavily, then I can easily fill up to 1,500 litres of water in half an hour. This will easily last my family a week or so,î says Puri. "When there is excess rainfall, then I use the overflow to recharge my well, which is in my garden. I use the water in the well to get through the dry season."

"The need for rainwater harvesting in a country like Nepal is acute," says Madhav Prasad Dhakal, a associate hydrologist at ICIMOD. "There is a severe water shortage in our urban areas, but there are also alternatives like water tanker trucks for people who can afford such facilities. In rural areas, however, there are no such provisions, and it makes sense for people to turn to rainwater." ICIMOD has built large-scale rainwater-harvesting systems in Kavre, Surkhet and Kalikot. Another organisation, Helvatas, has constructed around 200 rainwater harvesting systems in Dailekh. "Most settlements in Nepal are built on hills, far away from freshwater sources like rivers and where the groundwater table is very low. To utilise rainwater is the best option we have for solving our water problems," says Dhakal.

Why hasn't rainwater harvesting taken off?

Rainwater harvesting is feasible all over Nepal for two reasons: one, storing only a few months worth of rainwater allows Nepali users of most locations to be self sufficient; and two, filtration of rainwater requires no electricity or chemicals and can be consistently filtered to WHO quality drinking standards. These features in combination are unique to rainwater as a source--as opposed to groundwater (from wells), or jar water, or those delivered in tanker trucks, or even the water sourced from government mains.

"Harvesting rainwater solves the many daily discomforts Nepali people face owing to accessibility of water. What a Nepali considers water woes depends on where they live or their socio-economic status. For instance, for an upper/middle class Kathmandu man, his water problem may pertain to the occasional lack of water for his showers; however, for a village girl responsible for lugging water for her family, access to safe drinking water is an important variable in her daily life," says Pradhan of Best Paani.

But despite all these problems to do with water availability, the number of people who practice rainwater harvesting is minuscule. "There are numerous reasons for this. First, there is a lack of awareness among the people," says Shakya. "They feel they don't have the time for setting up a system. Second, they feel it is costly. Third, people are hesitant to use rainwater, thinking it is impure. But rainwater is the second-best form of water, after spring water. It is soft water. Of course, we do have to filter it, but that's not an impediment. The fourth problem has to do with the government's lack of efforts in this regard. And finally, we humans are lazy creatures, and these systems require at least some care and attention."

By 2050, two-thirds of the world's population will be living in cities, and demand for water is expected to grow in direct proportion to the urbanisation happening in developing countries. This means that access to safe drinking water will decrease in the fastest growing urban areas. The Kathmandu Valley continues to urbanise at an exceedingly breakneck pace and its many new denizens, and older ones too, would do well to turn to rainwater harvesting, say experts such as Shakya.

"There is so much water--falling freely from the sky--but we pay little attention to it," says Shakya. "And many of us still don't know that we can completely depend on it for our water needs."

An eco-friendly restaurant, Tasneem's Kings Kitchen, at Pulchowk, is one of the few restaurants in town that promotes and practises rainwater harvesting. "When I started constructing this place, I wanted to be water-sufficient. That's why I decided to invest in rainwater harvesting," says Tasneem Sahani, owner of the establishment. The restaurant has a reservoir with a capacity of 7,000 litres. During the dry seasons, Sahani has to make do with water tanker trucks. "But I do prefer drinking the water that I have harvested," says Sahani. During the rainy season, an hour or two's heavy downpour can fill her reservoir. As for the overflow, her groundwater recharge system allows the water to be collected in the well in her compound. Sahani uses some of the harvested rainwater for washing the dishes and cleaning. The water that she uses for cooking and drinking, however, first goes through many levels of purification.

"The harvesting systems is a one-time investment. Earlier, I had to buy 3-4 tankers of water in a week. Now I only have to buy one, says Sahani. My customers too are happy about our using rainwater, and if my customers are happy so am I."