Bangladesh is a country with a population of more than 160 million. The majority of its people face acute crisis of clean and drinking water. Surface water in the country is being continuously contaminated by both industrial and human pollutions, with demand for this vital component of life increasing fast due to rise in population. Besides, rapid increase in population results in withdrawal of groundwater at a faster rate than it is replenished by recharge.
The increasing strain on water resources has led to an immediate need to find innovative technologies without undermining the ecosystem. Therefore, where there is no surface water, where groundwater is deep or inaccessible due to hard ground conditions, or where it is too salty, acidic or otherwise unpleasant or unfit to drink, another source must have to be sought.
In this daunting situation, sustainable management of fresh water can be a proactive approach by ensuring proper utilisation of alternative water sources. Therefore, in the areas which have regular spells of rainfall, the most appropriate alternative is rainwater harvesting. By using this method effectively, we can easily meet the current demand for potable water to some extent and also be able to use it for industrial purpose. It will require green technology to ensure eco-friendliness.
In the past, rainwater harvesting was thought to be useful quite often merely for irrigation purpose. With the passage of time, the traditional concept regarding rainwater harvesting has changed; and it is now considered to be a valuable resource as it has been finding its industrial uses indoors in meeting demands for non-potable water.
Rainwater harvesting puts the supply of water back to normal levels. It is the collection and storage of water from surfaces that rain has fallen upon. In a normal scenario, the rainwater is collected from building roofs and then stored in a special tank. Rainwater harvesting systems are designed after assessing site conditions that include rainfall pattern, occurrence of rainfall, subsurface strata and their storage characteristics. Rainwater harvesting is popular all over the world. Potable or drinking water, a renewable but inadequate resource, is scarce in many areas of the developing world because of unplanned withdrawal of water from rivers and underground aquifers causing acute environmental problems like arsenic contamination. In many countries, the amount of water being consumed has exceeded the annual amount of renewal creating a non-sustainable situation. In addition to that, rainwater run-off during rainfall from roofs and other sealed surfaces during heavy rain are leading to accumulated flooding in the urban areas of many countries like Bangladesh, where the drainage system is not designed by keeping in mind the volume of rainwater runoff.
It is also significant to highlight that rainwater harvesting is a low-cost alternative potable water supply option in the coastal region of Bangladesh, which is considered one of the most vulnerable countries in the world due to its radical climate change and the resulting sea-level rise. As a result of the increasing salinity intrusion, drinking water scarcity becomes severe in the south-western coastal region of the country.
At this point, rainwater harvesting can be a blessing for the people of the coastal belt. Let us focus on Patkelghata in Satkhira district of Bangladesh. The Satkhira district averages nearly 1,710 mm rainfall per year. Based on the rural housing pattern of this region, a rainwater harvesting system is proposed here. It consists of roof catchments, gutters, down pipes, first flush devices, filter chambers and storage tanks. The catchment area is assumed to be 6m2 with the storage tank having 2000-litre capacity. Data have been collected on the present state of fresh water supply, sources and quality, average rainfall in the region, dry spell period, family size, water use nature, rainwater quality and material to be used for storage, etc. Rainwater quality has also been tested and the parameters found to be within Bangladesh's standard limit. After a detailed calculation, an approximate cost was assumed to be at $171 for building and operation of the whole system. A questionnaire-survey has also been conducted on views and opinions of the local people in understanding the problems, prospects and the popularity of rainwater harvesting in Bangladesh. As Bangladesh has a warm and humid tropical monsoon climate, here rain falls almost every month of the year except in the winter season. It is easy to design a sustainable rainwater harvesting system for domestic uses. Theoretically, rainwater harvesting and reuse has a number of tangible benefits:
* Rainwater harvesting is a useful method to keep ecological balance.
* Relatively cheap materials can be used for constructing containers and collection-surfaces.
* Construction methods are relatively straightforward.
* Low maintenance costs and requirements.
* Collected rainwater can be consumed without treatment, if a clean collecting surface has been used.
* It is an ideal solution to water problems in areas having inadequate water resources and helpful in mitigation of the effects of drought.
* It is a free source of water that can be obtained with something as simple and inexpensive as a rain barrel collecting rooftop runoff.
* It can reduce the load on storm water systems.
* It can decrease the use of potable municipal water.
* A lot of energy is required to obtain, clean, and transport water; if demand decreases as a result of rainwater harvesting, less energy will be required.
However, rainwater harvesting isn't without controversy. There are few issues on the flip side:
* Supplies can be contaminated by bird/animal droppings on catchment surfaces and guttering structures unless they are cleaned/flushed before use.
* Poorly constructed water jars/containers can suffer from algal growth and invasion by insects, lizards and rodents. They can act as a breeding ground for disease vectors if they are not properly maintained.
But considering its merits and demerits we can definitely go for rainwater harvesting method to transform a waste product (storm water) into a precious resource. However, the amount of water collected is restricted by weather. For urban areas, in order to get enough rainwater, every home would need to have its own collection system for the use of flushing purpose.
In the industrial sector, those who want to put in place the eco-friendly green technology must have to achieve green building certification from relevant authorities. Rainwater harvesting mechanism for industrial purpose is somehow different from the domestic uses. Harvesting LEED (Leadership in Energy and Environmental Design) Points Using Rainwater is presented in Figure 1.
It shows nearly half of the runoff from a 2-inch rainfall on a 30,000 square-foot site could be captured and used by a simple rainwater harvesting system. A system that employs a hydrocarbon filtration to treat runoff from parking areas could potentially capture significantly more runoff during most of the storms in the year. To ensure unparallel LEED Efficiency, a rainwater harvesting system is an efficient, effective tool that can be used to help harvest an impressive one-third of points needed for LEED certification, as is shown in Figure 2.
It is important to the facility owners, architects, engineers and others involved in building design and construction projects to determine how rainwater collection, storage, and distribution systems can help achieve over one-third of the points needed for "certified" status in the LEED 2009 for New Construction and Major Renovations (NC+MR) Green Building Rating System. This document also presents evidence showing how rainwater harvesting systems benefit the urban environment and help new buildings comply with emerging water use legislation. LEED 2009 Rainwater Harvesting Benefits are given below:
* Protection of water resources
* Reduction of storm water runoff and pollution
* Reduction of water/sewer bills
* Demonstration of sustainability
* Obtaining LEED® Credits
Rainwater Harvesting Design Considerations, according to LEED (V3), are given in the Figures 3 and 4.
IN Bangladesh, as the total ecosystem as well as the biodiversity is being affected due to water quality, the authorities concerned should formulate Clean Water Act following rainwater harvesting strategies in order to stop water contamination and ensure pure drinking water for all. Various water quality parameters in Bangladesh have deteriorated 16 to 20 times in recent times compared to those few decades back. Every day, industries are polluting water. Sixty per cent of the capital Dhaka's contaminated water comes from industrial units; thirty per cent is released by Dhaka WASA and the rest comes from Dhaka City Corporation. It is estimated that seventy per cent infant mortality is caused by lack of safe water supply, which could be prevented just by ensuring safe supply. Due to the increasing volume of industrial waste generated all over the world, finding efficient and cost-effective treatment methods to remove pollutants is increasingly being studied as a method to supplement limited fresh water resources in different countries. Most of these techniques are only suitable for pre-treatment industrial waste-polluted water. A more efficient technology should be employed when these waters are to be reused. Furthermore, to produce high-quality treated water for recycle and re-use, a series of different technologies should join together.
It is high time the government took innovative steps to convey the message of usefulness of rainwater harvesting. There should be an awareness campaign. For interested persons the government can arrange loans on easy terms. Being a country of abundant rainfall, Bangladesh could emerge as an ideal place for this eco-friendly system to be in use at mass level.
The writer is Sr. Assistant
Secretary, BKMEA.
ranaduttabkmea@gmail.com
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