Rain Water Harvesting: An Opportunity for Bangladesh

Captain Arif Mahmud

Bangladesh is a land of rivers. Numerous rivers, streams and canals flows crisscrossing the country. It is endowed with plenty of surface and groundwater resources. The surface water resources comprise water available from flowing rivers and static water bodies such as ponds, marshes and swamplands. The country receives plenty of rainfall and the amount of annual rainfall ranges from about 3200 mm in the northeast to about 1600 mm in the southwest region. The country has a subtropical monsoon climate characterized by wide seasonal variations in rainfall, high temperatures and humidity. Theoretically there are three distinct seasons in Bangladesh: a hot, humid summer from March to June; a cool, rainy monsoon season from June to October; and a cool, dry winter from October to March but in reality the situation is little different.

In recent years due to climate change factors, sometimes the rain starts in early April and goes on till October but normally the rain is not much in March, April and May and thus these months are very hot and dry and affects the human beings and the land as well. Moreover very little amount of water released through the Padma river which affects the north-eastern part of the country. The ground water level goes down, the cultivatable land mass get seriously affected by drought. The scarcity of water makes human lives very hard.

In Bangladesh, surface water was the principal source for drinking water ever up to recent past. However, during the recent decades, due to the intensive development programs, the ground water is utilized for drinking purpose in most rural areas. Unfortunately, recent investigations have demonstrated almost countrywide occurrence of high arsenic levels in the tube well water. Today, Bangladesh seems to be one of the most arsenic affected countries in the world, Bangladesh is a tropical country and receives heavy rainfall during the rainy season. In the present context, rainwater harvesting is being seriously considered as an alternative option for water supply in Bangladesh. The rain water is free from arsenic and other impurities and if treated properly it can be made germ free.

Rain water harvesting:

Rainwater harvesting and storage is not a new technology. It has been used for domestic and agricultural purposes for a longtime. Historical sources mention the use of rainwater for drinking water supply some 4000 years ago in the Negev desert, close to present day Jordan.  Interest in the use of rainwater as an alternative or supplemental source of water for domestic water supply has been stepped up recently. In developing countries where due to a number of problems, availability of adequate and drinking water within easy reach is not always assured. Also, the cost of supplying water to the people through pumping, gravity or other schemes is quite expensive. The rainwater harvesting is considered as a possible answer to the global water use problem, especially where surface and groundwater are limited.

There are various types of rainwater catchment systems available and some of them are easily applicable to our country in cities and even in villages. Only few things to be fixed with the roofs to catch the water and a tank for collection. All these water can be directly used for washing purposes but for drinking and cooking either the water has to be boiled or some form of filtration will be necessary.

Rain water harvesting for small houses

This is the most common type of rain water catchment system and can be easily installed all over our country especially with any type of small hut.

The rain water will fall on the roof and through system of gutter and pipe will be collected in storage tank. Filters can be used to remove dust, sand and other physical impurities.

It is a good practice to let the water wash the roof and pipes initially for few minutes and then open tank for collection of water. The rainwater is arsenic free but if it mixes with dust particles then there will be a danger of arsenic transfer from the sand or dust particles into water. For drinking and cooking this water has to be boiled or filtered through reverse osmosis or chlorination system to remove germs. In many parts of our country there is scarcity of drinking water and in the southern part of our country the rivers and canals are infested with salt water. For those places this rain water can be collected in big reservoirs for use throughout the year. The rainwater does not contain essential salts and minerals required for human body so little amount of various salts and other minerals are required to be added to make the rainwater healthier.

The system for the multi storied buildings are quite similar to the previous system. The rainwater will be collected on the roof and will be collected to a suction tank on the ground through a number of pipes. A filter will be fixed in this tank to remove the impurities from rainwater.  From suction tank the water will be transferred to a collection tank. The collection tank may be fitted with level sensor switches. When the level of the water goes high the float switch will start the transfer pump and send water to the roof top tank of the apartment and this water will be used by all the people living in the complex. It will be a good practice to initially drain the water to get rid of impurities for few minutes and then start the collection of rain water. This water can be directly used for all the washing purpose but for drinking and cooking this water should be boiled or filtered with reverse osmosis or chlorination process. The rainwater does not contain many essential salts and minerals so it may be required to add salt and minerals with rainwater to make it healthier.

The benefits of rainwater harvesting system are:

– Less cost.

– Helps in reducing the water bill.

– Decreases the demand for water.

– Reduces the need for government water supply.

– Promotes both water and energy conservation.

– Improves the quality and quantity of groundwater.

– Does not require a filtration system for landscape irrigation.

This technology is relatively simple, easy to install and operate.

It reduces soil erosion, storm water runoff, flooding, and pollution of surface water with fertilizers, pesticides, metals and other sediments.

It is an excellent source of water for landscape irrigation with no chemicals and dissolved salts and free from all minerals.

The rainwater harvesting in Bangladesh cab be a possible alternative for drinking water source both for urban and rural areas. There is adequate rainfall during the rainy season. The water quality of rainwater is very high and the stored water quality is also very satisfactory when proper attention is given during collection. This water is free from arsenic. Rain water can be directly used for washing purpose but for drinking it should be boiled or made germ free by other means.

The major advantage of the rooftop rainwater harvesting system is that the system is independent and suitable for scattered settlements. Each household can use their own separate water storage system. It is very convenient for the users especially for the women to collect water from their house premises. It saves the time of collecting water from a distance source. As the system is household based, strong community cohesion is not a very prerequisite factor for rain water harvesting.

The operation of the rainwater harvesting is easier than any other water supply system. No specialized skills are necessary to operate the system. It does not require any pumping device to collect rain water. The system also requires very little maintenance work. The maintenance work is mainly cleaning the catchment area, gutters, down-pipe, storage tank etc. The storage tank can require plastering or other maintenance work, normally once in five years if the storage tank is constructed properly. The success of the rainwater harvesting system depends on the interest, enthusiasm and active support of the users.

Groundwater is the main source of water supply in Bangladesh in recent years.  Most of the people of our country are hesitant about the use of rain water. The rainwater harvesting program can only be implemented when people have the willingness to use the system. The community must be involved in such projects. By watching the economic success of the project in one house, the neighbors will get interested and they will become to employ such system in respective houses. 

One of the important steps towards achieving a successful and suitable rainwater harvesting system is to create awareness of the technology among its potential users. This can be achieved through mass media, workshop and grass root level formal and informal meetings. The community must be involved in the planning, design, siting and construction of the rainwater harvesting. Women should be encouraged in using this system for their house hold use.

No one can deny the necessity of water in our daily life. In spite of being called the Ganges Delta, many places of Bangladesh suffers from the scarcity of water, especially in dry seasons.  People need to travel for long distances to collect water and it may not be always possible to collect clean and germ free water. The rain water harvesting can be a solution for all those sufferings. Clean water can be collected in big reservoirs to be used in the dry seasons especially for drinking and cooking. The rain water harvesting can save the ground water reserve and also all the energy spent for the transmission of especially in urban areas.

Author is an Assistant Professor of  Maritime Science Department at Bangabandhu Sheikh Mujibur Rahman Maritime University, Dhaka, Bangladesh

Email: arif.nautical@bsmrmu.edu.bd

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