Water supply in Bangladesh is primarily based on groundwater sources. In the context of very high prevalence of diarrhoeal diseases in Bangladesh, bacteriological quality received priority as a criterion for drinking water supply. Groundwater is free from pathogenic microorganisms and available in adequate quantity in shallow aquifers for development of low-cost tubewell based water supply for scattered rural population. Bangladesh achieved a remarkable success by providing 97% of the rural population with bacteriologically safe Tubewell water. This is the largest population coverage in the region. Unfortunately, when the rural people have developed the habit of drinking tubewell water being aware of its importance to avoid diarrhoeal diseases, arsenic in excess of acceptable limit has been found in tubewell water in many parts of Bangladesh.
At present, the success achieved in hand tubewell based rural water supply is on the verge of collapse due to presence of arsenic in groundwater in excess of acceptable levels in the shallow aquifers. It has now been estimated that about 29 million people in Bangladesh are drinking water with arsenic in excess of 50 m g/L. Arsenic in excess of 50 m g/L is considered unsafe in Bangladesh. Thus arsenic problem alone has reduced the national population coverage by safe water supply from 97 percent to 74 percent. Provision of arsenic contamination free water is urgently needed for mitigation of arsenic toxicity and protection of health and well being of the rural population living in acute arsenic problems areas. The people, particularly the women living in the problem areas have to walk long distances to fetch water from an available safe source.
The main sources of water in Bangladesh are surface waters in rivers, reservoirs, lakes, canals and ponds and groundwater in shallow and deep aquifers. Both ground and surface water sources are dependent on each other. Many streams receive a major portion of their flow from groundwater. Elsewhere, water from surface streams is the main source of recharge for groundwater. In general, groundwater flows into the surface water sources in dry season and surface water enters into ground during monsoon. The two sources of water are interrelated and the use of one usually affects the water available from the other source. In recent years, large-scale use of groundwater for irrigation purpose has caused lowering of groundwater level and drying up of surface water sources. Rainwater is an alternative source of water available in adequate quantity in the wet season of the year. The average yearly rainfall in Bangladesh is around 2450 mm, which is a major source of water for the replenishment of both surface and groundwaters.
The surface and groundwaters available in Bangladesh are abundant but the quality of water of these sources has become the main constraint for the development of safe and affordable water supply systems. The surface water sources are being misused as a sink for highly polluting waste waters from domestic and industrial sources. The pollution loads far exceeding assimilation capacities have caused severe degradation of water quality. Poor surface water quality compelled the water supply authorities and agencies to develop groundwater based water supply systems and achieved a remarkable success by providing tubewell water to almost all. The presence of arsenic in groundwater has now become the major water supply problem in Bangladesh. In the coastal belt, high salinity in surface and ground waters and in the hilly areas, absence of good aquifers as well as difficulties in tubewell construction in stony layers are the main constraints for the development of a water supply system. Groundwater lowering in the dry season is drying up the suction mode handpumps causing severe water supply problem in many areas of Bangladesh.
Arsenic toxicity has no known effective treatment, but drinking of arsenic free water can help arsenic affected people at early stage of ailment to get rid of the symptoms of arsenic toxicity. The most important measures needed is to prevent further exposure by providing safe drinking water. Based on the current situation and information available, some options can be identified to provide safe drinking water. These include uncontaminated shallow tubewells, dug/ring wells, arsenic free water from deeper aquifers, rainwater harvesting, pond-sand filters, household treatment of arsenic contaminated water, and piped water supply from safe or treated sources. Most of the deep tubewells are arsenic contamination free and a deep tubewell underlain by an impervious clay layer is not likely to be contaminated in near future. Possibility of arsenic contamination of uncontaminated shallow or deep tubewells in future cannot be excluded. However, monitoring of groundwater for arsenic content at regular interval is absolutely essential for groundwater based water supply in Bangladesh.
In the present context of emerging water supply problems, the water supply situation, nature of problems and alternative options to meet the present and future needs require critical evaluation. The analysis of availability of water, quality of water, technological options for safe water supply and people’s participation is essential for the development of sustainable water supply systems in arsenic affected areas.
The purpose of this document is to compile available information to enable the participants of the workshop to arrive at considered opinion in respect of:
This document has been organized with an introduction to the problem in section 1. The second section deals with in details the water supply and arsenic contamination situation with adequate information about sources of water supply with associated problems. All the alternative water supply technologies including the technologies for arsenic removal tried in this country have been briefly described in section 3. The experiences of different organizations involved in arsenic-safe water supplies have been discussed in section 4. The section 5 presents some thoughts on institutional arrangements for delivery mechanism and sustainable use of these technologies. Recommendations including future research and development needs in alternative water supply options have been presented in section 6.