Rainwater harvesting Seeking a sustainable solution for water crisis -Nazmunnaher Nipa

There is nothing more important than water for survival. That is why 71 percent of the earth is covered by water. But most of it is salt water that we can’t use in our daily work. Not just humans, all living things in the world need water to survive. It is an essential element of our ecosystem. Although the earth has plenty of water and its sources are renewable, the availability of water is not same everywhere.
Every day Dhaka WASA supplies 250 crore liters of water to the metropolis. Eighty percent of this water comes from the ground.This water is being supplied through installation of deep tube wells in different parts of the city.Due to groundwater abstraction, the water level is going down by two to three meters every year.
Rainwater harvesting is one of the feasible options of fresh water sources in the coastal areas of Bangladesh and recently a lot of initiatives and programme were undertaken to promote and install rainwater harvesting systems both in the coastal and arsenic affected areas in Bangladesh. Moreover, every year the country is also blessed with ample rain. The average annual rainfall in Bangladesh is about 2200 mm, seventy-five percent of it occurs between May and September.

Water resources management in Bangladesh faces immense challenge for resolving many diverse problems and issues. The most critical of these are alternating flood and water scarcity during the wet and the dry seasons, arsenic contamination, salinity, ever-expanding water needs of a growing economy and population.
According to a study by the Institute of Water Modelling based in Bangladesh’s capital city, its groundwater level is falling by three meters per year. Population has increased and industry has expanded, river water has become contaminated with industrial waste. Today, groundwater is expected to satisfy over 80% of the city’s water supply. About 150bn liters of rainwater could be harvested during the monsoon season in Dhaka city alone.

Rainwater harvesting is therefore a potential option of water supply to the coastal and arsenic affected rural communities in Bangladesh. Rainwater harvesting, low-cost systems that collect and store rainwater for year-round use, offers a cost-effective and practical solution to ease water crisis.
In a recent seminar, international NGO WaterAid and The Institute of Engineers, Bangladesh concluded that rainwater harvesting needs to be included in establishing the country’s bylaws. Therefore, In the recent years from 2000-2004, a lot of programs and huge investments have been done by government organization and NGOs with the financial support from international donor agencies to promote and install several types of household and community based rainwater harvesting systems both in the coastal and arsenic affected areas in Bangladesh as an alternative water supply sources other than groundwater. Since 1997, about 1000 rainwater harvesting systems have been installed in the country, primarily in rural areas (UNDP).
Rainwater harvesting as an option can be adopted in order to facilitate availability of safe and affordable drinking water supplies and to preserve natural depressions and water bodies in major urban areas for recharge of underground aquifers.

Arsenic Contamination
Arsenic contamination of ground water affects many rural areas, whilst some urban areas including the capital, Dhaka City, lack sufficient potable ground water to meet the demand. As a result, population heavily dependent on hand pumps and tube wells are exposed to arsenic related serious health risk. World Health Organization described the arsenic contamination in Bangladesh as “the largest mass poisoning of a population in history”.

Salinity
Bangladesh has very long coastlines and coastal area covers 20,000 square km area. In the coastal areas, aquifer conditions are not suitable for shallow tube well and high salinity in both surface and groundwater are the main constraints for the development of a dependable water supply system. Traditional rainwater harvesting for drinking purposes in a limited scale has been the common practice for long time and in some areas of the coastal region with high salinity problem. About 36 percent households have been found to practice rainwater harvesting in the rainy season for drinking purpose and domestic needs.

Fluoride Concentration
Recently there has been some concern about fluoride in drinking water in Bangladesh. In some rural areas of Bangladesh, the fluoride concentration in water is reported higher than maximum permissible limit (MPL). In rural areas, where the drinking water is drawn from available sources such as tube wells, hand pumps or ponds, in which the fluoride concentration may exceed the MPL.

Rainwater harvesting and sustainable water strategy:
Restoring the Hydrological Cycle- Due to the rapid pace of urbanization, many of the world’s large cities are facing problems with urban floods. The natural hydrological cycle manifests itself at different scales, depending upon climatic, geographic and biological factors. As rain falls over time and seeps underground to become groundwater, it feeds submerged springs and rivers. The concrete and asphalt structures of cities have tended to disrupt the natural hydrological cycle, and reduce the amount of rainwater permeating underground. A decrease in the area where water can penetrate speeds up the surface flow of rainwater, causing water to accumulate in drains and streams within a short time. Every time there is concentrated heavy rain, there is an overflow of water from drains, and small and medium sized rivers and streams repeatedly flood. These conditions can often lead to an outpouring of sewage into rivers and streams from sewer outlets and sewer pumping stations, thus contaminating the quality of urban streams and rivers.

Dhaka Water Supply and Sewerage Authority (WASA) have shown that rainwater is free from arsenic contamination and the physical, chemical and bacteriological characteristics of harvested rainwater represent a suitable and acceptable means of potable water. In urban areas, at a household level, rainwater can be used for flushing toilets, watering gardens and washing floor and these uses are known as non-potable. While in rural areas, it becomes the main source of water for potable uses which include drinking, bathing, and cooking.
In Bangladesh, rainwater collection is seen as a viable alternative for providing safe drinking water in arsenic affected areas. Since 1997, about 1000 rainwater harvesting systems have been installed in the country, primarily in rural areas, by the NGO Forum for Drinking Water Supply &Sanitation. This Forum is the national networking and service delivery agency for NGOs, community-based organizations and the private sector concerned with the implementation of water and sanitation programmes in unsaved and underserved rural and urban communities. Its primary objective is to improve access to safe, sustainable, affordable water and sanitation services and facilities in Bangladesh.
The rainwater harvesting tanks in Bangladesh vary in capacity from 500 liters to 3,200 liters, costing from Tk. 3000-Tk.8000 (US$ 50 to US$ 150). The composition and structure of the tanks also vary, and include ferro-cement tanks, brick tanks, RCC ring tanks, and sub-surface tanks. The rainwater that is harvested is used for drinking and cooking and its acceptance as a safe, easy-to-use source of water is increasing amongst local users. Water quality testing has shown that water can be preserved for four to five months without bacterial contamination. The NGO Forum has also undertaken some recent initiatives in urban areas to promote rainwater harvesting as an alternative source of water for all household purposes.

Advantages of Rainwater Harvesting Include:
l Rainwater harvesting can reduce storm drainage load and flooding in city streets.
l Users of rainwater are usually the owners who operate and manage the catchmentsystem, hence, they are more likely to exercise water conservation because they knowhow much water is in storage and they will try to prevent the storage tank fromdrying up.
l Rainwater harvesting technologies are flexible and can be built to meet almost anyrequirements. Construction, operation, and maintenance are not labour intensive.
l Rainwater harvesting can co?exist with and provide a good supplement to other watersources and utility systems, thus relieving pressure on other water sources.
l Rainwater harvesting provides a water supply buffer for use in times of emergency orbreakdown of the public water supply systems, particularly during natural disasters.
Rainwater harvesting has been practiced for more than 4,000 years in most of the countries, owing to the temporal and spatial variability of rainfall. It is an important water source in many areas with significant rainfall but lacking any kind of conventional, centralized supply system. It is also a good option in areas where good quality fresh surface water or groundwater is lacking. The application of appropriate rainwater harvesting technology is important for the utilization of rainwater as a water resource.

Nazmunnaher Nipa is an Associate Editor of The Environment Review.