2. WATER SUPPLY SITUATION ANALYSIS
 
 
 

2.1 SOURCES OF WATER

1. General

2.1.2 Surface Waters

Availability

Surface water is abundant in the wet season in Bangladesh. An estimated 795,000 million cubic meter (Mm³) of surface water is discharged through the Ganges-Brahmaputra system, in the downstream of the confluence of the Ganges and the Brahmaputra. This is equivalent to 5.52 m deep water over a land area of 144,000 km². There are other rivers discharging surface water into the Bay of Bengal. An average annual rainfall of 2.40 m within the country partly replenishes surface water sources. Each year about one-third of Bangladesh is submerged in a normal flood, and the area submerged may increase to about two-thirds during severe floods. In the dry season water scarcity persists in many areas. In this period surface water is only available in part of the 22,155 km of major rivers, 1,922 km² major standing water bodies and about 1,475 km² of ponds in the country. Surface water irrigation systems in the country compete for this available water in the dry season. The perennial water bodies are decreasing with the use of more and more surface water.

Traditionally, before and during the early stages of tubewells installation, rural water supply was largely based on protected ponds. There are about 1,288,222 ponds in Bangladesh having an area of 0.114 ha per pond and 21.5 pond per mauza (BBS, 1997). About 17% of these ponds are derelict and probably dry up in the dry season. The biological quality of water in these ponds is extremely poor due to unhygienic sanitary practices and absence of any sanitary protection. Many of these ponds are chemically and bio-chemically contaminated for fish culture. If one pond per mauza could be protected from contamination, it would provide a source of drinking water with minimal treatment and water for other domestic uses without treatment. The Government of Bangladesh has greatly emphasized the development of protected pond-based water supply systems. The protected ponds should not receive any surface discharge and should only be replenished by rain and groundwater infiltration.

Problems

Surface waters receive pollutants from agricultural, industrial, domestic and municipal sources. Concentration of silt content in turbulent water in the monsoon is high. Similarly algal growth in stagnant water bodies in the dry season is also very high. Insanitary practices of people have greatly contributed to the deterioration of quality of surface water sources. The faecal coliform concentration in most surface water sources lies in the range of 500 to several thousand per 100ml. The rivers and surface water sources around densely populated urban areas depending on water quality parameters are four to ten times more polluted than the similar water sources in the countryside. The deterioration of water quality is directly related to population density and industrial activities due to poor management of domestic and industrial wastewater. The use of surface water for drinking purpose requires clarification and disinfection by elaborate treatment processes. The availability of surface water in the dry season is also a constraint for the development of dependable small and large scale surface water treatment plants for water supply.
 
 

2.1.3 Groundwater

Availability

Groundwater is the most important source of water supply in Bangladesh. Except for few hilly regions Bangladesh is entirely underlain by water-bearing aquifers at depths varying from zero to 20 m below ground surface. The soil is mostly stratified and formed by alluvial deposits of sand and silt, having occasional lenses of clay. The main constituent of the aquifer materials is the medium-grained sand deposited at the lower reach by the mighty rivers - the Ganges, the Brahmaputra and the Megna with their tributaries. Groundwater can be easily abstracted by installation of wells for the development of water supply systems. The water abstracted for various purposes is replenished in the monsoon.

Physically groundwater is generally clear, colorless with little or no suspended solids and has a relatively constant temperature. Groundwater is also free from disease-producing micro-organisms which are normally present in large numbers in surface waters. The slow filtering action of fine-grained soil through which the surface water percolates to join the groundwater removes almost all suspended impurities. Moreover, the lack of oxygen and nutrients in groundwater makes it an unfavorable environment for disease-producing micro-organisms to survive, grow or multiply. On the other hand, being a universal solvent, water dissolves many of the minerals present in earth’s crust during its slow travel through the ground. Anaerobic conditions in soils in some flood plains, and the presence of organic acids and carbon dioxide increase the solubility of groundwater. As a result, groundwater may contain minerals in varying concentrations depending on soil conditions. Arsenic contamination of groundwater is believed to be the result of such reactions in the adverse geoenvironment.

In the context of high prevalence of diarrhoeal diseases in Bangladesh, groundwater received priority as a source of water supply because it is generally free from pathogenic micro-organisms. Almost all rural water supplies and most of urban water supplies are groundwater based. Groundwater collected by tubewells is fit for consumption. Groundwater abstracted from shallow aquifers by hand tubewells has received acceptance in rural areas for drinking purposes, but due to its high iron content, hardness, etc. people do not want to use hand tubewell water for other domestic purposes like cooking, bathing and washing. The high iron in groundwater makes the cooked food blackish in colour and produces stains on utensils. The hard water requires more soap for washing.

Aquifer characteristics

The available geological information and related studies have shown that two types of aquifers exist in Bangladesh. A shallow aquifer which has been termed as "main aquifer" lies within 100 m from the surface with an overlying clay/silt blanket which is less than 2 m thick in the northwest and generally increases southward to more than 50 m. Other deep aquifers whose water development potential is not known occur at depths between 300 and 2500m. In the majority of alluvial basins, the thickness of top clay and silt layers varies between 5 and 15m. In the extreme northwest this layer does not exist and silty to fine sand occurs at the surface, while in the Madhupur and Barind Tracts as well as in Chittagong District, the thickness of this layer is greater than 35m.

In the shallow aquifer, groundwater flows from north to south with localized outflow into the major rivers. Groundwater gradient varies from 1:1,000 in the northwest to 1:13,000 in central Bangladesh to less than 1:20,000 in the coastal area. Permeabilities of the aquifers are high and vary from 10 to 200 m/day. Transmissibilities of the main aquifer range from 100 to 10,000 m²/day with an average value of 2,000 m²/day (MPO, 1991). Although the aquifer has high transmissibility the horizontal flow of groundwater is very low because of the low groundwater gradient. The storage capacity of the aquifer in Bangladesh increases with depth because of the increase in the size of aquifer materials. The specific yield varies from 0.02 to 0.25 m³ per m³ of aquifer materials.

Groundwater situation

Groundwater in Bangladesh, except in some places, is available at a shallow depth. Groundwater levels are at or near ground level during the period August-October and lowest in April-May. Groundwater rises as a result of recharge during May and usually reaches its highest in late July in each year. Between July and October groundwater levels are constant and maintain a balance between surface water levels and the fully recharged aquifers. Groundwater levels fall from October in response to rapid drainage of surface water and changes in base levels. The rate of fall is highest in October-November but equally large changes may take place after January when withdrawal of groundwater for irrigation starts. During the dry season most of the minor rivers are sustained by groundwater outflows.

There are several areas of Bangladesh where groundwater withdrawals are causing a large decline in groundwater levels during dry seasons. Recharge during the wet season enables the groundwater levels except in Dhaka and Comilla areas to recover to their normal level. The groundwater withdrawal and recharge characteristics suggest that the actual recharge can be increased approaching the potential limits by creating additional storage through increased abstraction during the dry season. This process severely restricts the development of suction-mode tubewells, however. According to MPO (1991) estimates, out of 42,543 Mm³ total useable recharge, 40% is available through shallow tubewells. A study shows that 349 upazilas can adequately allow groundwater development by handpump tubewells of which 197 upazilas having groundwater level within 4.5m of the surface in dry season allows groundwater abstraction by suction mode No.6 pump. In 60 Upazilas, the groundwater level lies within 4.5m to 6.5m, the marginal range for forced mode Tara pump. In 92 Upazilas the water level falls below the limit of suction mode pumps in the later part of dry season, but it is suited for forced type handpumps (DPHE and UNICEF, 1994).

Problems

Groundwater is the main source of water supply in urban and rural areas of Bangladesh. Groundwater in Bangladesh is available in adequate quantity, but the availability of groundwater for drinking purposes has become a problem for the following reasons:

• arsenic in groundwater;
• excessive dissolved iron;
• salinity in the shallow aquifers in the coastal areas;
• lowering of groundwater level;
• rock/stony layers in hilly areas.

4. Rain Water

Rainwater, available in adequate quantity in Bangladesh, is an alternative source of water supply in Bangladesh. The spatial distribution of normal rainfall in Bangladesh has been shown in Figure 2.1. The distribution of rainfall in Figure 2.1 shows that relatively higher rainfalls occur in the eastern part of the country and highest rainfalls occur in north-eastern region and eastern part of the coastal area. The low rainfall, less than 1500 mm per year, occurs in the western part of Bangladesh. In the coastal and hilly areas with greater intensity of fresh water source problem have higher rainfall, which is favourable for rainwater harvesting.

A 12-year rainfall pattern based on the mean rainfall intensity recorded in 28 stations for the period from 1987 to 1998 is shown in Figure 2.2 ( BBS, 1999). It appears that the average yearly rainfall in the country during 1987-96 varied from 1950 to 2900 mm i.e. 1.95 to 2.90 m³ of rainwater was available per m² of catchment area each year for development of a rainwater based water supply system. In many countries in world having half the rainfall of Bangladesh are practicing rainwater harvesting for water supply.

Problems

The availability of rainwater is limited by the rainfall intensity, distribution over the year and availability of suitable catchment area. The distribution of monthly rainfall over the year presented in Figure 2.3 shows that the 75% of the rainfall occurs during May to September and the excess rain in wet season is required to be stored in large tanks for consumption in the dry season. In Bangladesh 48% of the households have C.I sheet, tiles and pucca roofs suitable for the collection of rainwater (BBS, 1999). However, the poorer section of the people is in disadvantageous position in respect of utilization of rainwater as a source of water supply. This section of people has smaller size thatched roof or no roof at all, to be used as catchment for rainwater collection. The main problems of rainwater harvesting are easy access to surface and groundwater sources, lack of initiatives and management. Storage and maintenance of quality of water from bacteriological perspective are also significant problems in Bangladesh.

2.2 WATER SUPPLY SITUATION

Water supply in Bangladesh and India started during the early stage of the development of water supply. The water supply in Dhaka city was first started with the establishment of Dhaka Water Works (DWW) by the Nawab Sir Abdul Gani in 1874. Major water works in the sub-continent and even in the developed world started around that time. Although the first water supply in Bangladesh was surface water based, groundwater received priority in the subsequent development of water supply in the country. The surface water treatment plants operated by Dhaka Water Supply and Sewerage Authority (DWASA) in Dhaka and Narayangonj produce about 40 million litres per day (DWASA, 2000).The Mohora surface water treatment plant in Chittagong is the largest surface water treatment plants in Bangladesh producing about 90 MLD of water. There are few small surface water treatment plant and quite a large number of Pond Sand Filters for treatment of mainly pond water in the country but the total quantity of water produced by these units is very small as compared to demand.

Schemes for the collection of groundwater through handpump tubewells for community water supplies in rural Bangladesh were taken up as early as 1928. In the context of very high prevalence of diarrhoeal diseases in Bangladesh, groundwater, being usually free from disease producing micro-organisms, received priority as a source of water for water supply. Since 1928, an estimated 6-8 million hand tubewells have been sunk in Bangladesh to provide drinking water to 97% of the population. The two main aquifers systems with intermediate impermeable layers and three main modes of tubewells based water supplies are illustrated in Figure 2.4.

The numbers of manually operated shallow and Deep tubewells sunk by DPHE are 894,941 and 81,384 respectively (DPHE, 2000). The people themselves to meet their demand for water supply have sunk the remaining tubewells.

The water supply in core area of 95 WS towns are primarily based on power operated relatively large diameter shallow and deep tubewell (DTW) usually called production well where as in the periphery 23 percent of the urban population is served with manually operated sallow tubewells (STW). The groundwater pumped by DTW in urban centres except Dhaka and Comilla are fully replenished in the wet season.

Because of high salinity in groundwater in shallow aquifers, the density of tubewells in the coastal area is much lower than that in the shallow tubewell areas. Manually operated small diameter deep tubewells are the main source of water supply in coastal areas. Based on the availability of fresh groundwater, the Department of Public Health Engineering has divided the coastal regions into three types of areas. These are shallow tubewell areas, deep tubewell areas and mixed shallow and deep tubewell areas. Shallow Shrouded Tubewells (SSTs) and Very Shallow Shrouded Tubewells (VSSTs) and Pond Sand Filters (PSFs) are alternative options of water supply in the coastal area. Recently, a few Rainwater Harvesting Systems has been constructed by different organizations in arsenic affected areas.

The population coverage by different modes of water supply has been presented in Table 2.1. The figures have been computed on the basis of data available from the Year Books of the Department of Public Health Engineering (DPHE, 2000), Sample Vital Registration System, Bangladesh Bureau of Statistics (BBS,1998), Water Supply and Sanitation Sector Questionnaire (UNICEF and WHO, 1999) and preliminary report on Population Census- 2001 of Bangladesh (BBS, 2001).

Table 2.1 : Population Coverage by Different Modes of Water Supply
 
 

Modes of Water Spply	Population Coverage, Million			Percent Coverage
	Urban	Rural	Total
Piped water supply	13.10	-	13.10	10
Manually operated Deep Tubewells	-	8.20	8.20	6
Manually Operated Shallow Tubewells	16.86	86.14	103.00	80
Dug/Ring Well	0.28	1.02	1.30	1
PSF, VSST, SST, Rainwater Harvesting	-	1.50	1.50	1
Others	-	2.15	2.15	2
Total	30.24	99.01	129.25	100

It is apparent from the figures in Table 2.1 that about 103 million people, which is 80% of the total population of Bangladesh depend on shallow tubewells for drinking water. A shift from shallow tubewell to alternative water supply options has become essential in acute arsenic problem areas. Prospective options are deep tubewell and development of surface water based water supply system like construction of community type Slow Sand Filters (SSFs) commonly known as Pond Sand Filters (PSFs). Slow Sand Filters are package type filter units developed to treat surface waters for domestic consumption in the coastal saline belt. In this system, surface water is discharged by handpump tubewell or by other means in a small reservoir underlain by a sand bed and the filtered water is collected through taps. The PSF is being promoted as an option for water supply in arsenic affected areas.
 
 

2.3 ARSENIC PROBLEM

1. Magnitude of Arsenic Problem

The study conducted by British Geological Survey (BGS), Department of Public Health Engineering (DPHE) and Mott MacDonald Limited (MML) in two phases examined 3534 distributed water samples from 61 districts (Except 3 hill districts) in an approximate grid of 6km x 6km. (DPHE, BGS and MML, 1999; BGS and DPHE, 2001). On an average 58 samples per district and 8 samples per upazila were analyzed. Although the sample number is smaller considering the variation of arsenic content within shorter distances, the study provides a reasonable distribution of arsenic contamination in Bangladesh. The study showed that arsenic concentration of 42% of all tubewell samples exceeded 10 m g/L and 25 % exceeded 50 m g/L. When only shallow tubewells are considered, 46% and 27% exceeded 10m g/L and 50m g/L respectively. In case of deep tubewell ( 150m ) samples, arsenic content of only 5% exceeded 10 m g/L and 1% exceeded 50m g/L. The maximum acceptable level in Bangladesh as per requirement of Bangladesh Standards for Drinking Water is 50 m g/L (GOB, 1997) and the provisional WHO guideline value for arsenic in drinking water is 0.01 mg/1 (WHO, 1993). The number of administrative areas with at least one sample exceeding Bangladesh Drinking Water Standard are shown in Table 2.2.

Based on the above study, Bangladesh Arsenic Mitigation Water Supply Project (BAMWSP) considers those Upazilas having at least one tubewell producing water with arsenic content exceeding Bangladesh Standard as arsenic contaminated Upazila.
 
 

The percentages of shallow tubewells yielding water of various concentrations of arsenic prepared on the basis of BGS/DPHE test results are shown in Figure 2.5. This diagram provides information about the percentage of shallow tubewells producing water in excess of corresponding concentration.

A map showing the intensity of arsenic contamination of groundwater in different parts of Bangladesh is shown in Figure 2.6. The map has been updated on the basis of information available from arsenic analysis conducted by BGS and DPHE (2001); DPHE,BGS and MML(1999); SOES and DCH, JU (2000) and BUET. The maps produced by other organizations based on field/laboratory test data more or less provide similar pictures of arsenic contamination.

It may be observed that the central regions of Bangladesh are highly contaminated. The levels of arsenic in tubewell water as shown in BGS and DPHE study are also high in the central region (BGS and DPHE, 2001). The area of high arsenic concentration very well fit with the areas of Bangladesh submerged by flood (Ahmed, 2000).

2.3.2 Population Exposed

The estimation of population exposed to arsenic contamination exceeding 50 m g/L in Bangladesh presented in Table 2.3. The computation is based on data available in the year books of the Department of Public Health Engineering (DPHE, 2000), percentage of shallow tubewells exceeding 50 m g/L as shown in Figure 2.5 based on groundwater studies for arsenic contamination in Bangladesh (BGS and DPHE, 2001) and preliminary report on the recently conducted population census (BBS, 2001).

The arsenic safe modes of water supplies are piped water in urban areas, deep tubewells (DTWs), uncontaminated shallow tubewells (STWs) and alternative water supply options such as pond sand filters, dug well, very shallow shrouded tubewells, rainwater harvesting etc. Arsenic contamination has been found in excess of national drinking water quality standards of 50 m g/L in 15 production wells supplying piped water to about 0.75 million in urban areas, 1% deep tubewells, and 27.4% shallow tubewells. The population exposed to arsenic contamination in excess of 50 m g/L by those tubewells has been estimated as 29.05 million. The total population exposed to arsenic is the sum of multiplication product of population served by each category and the fraction of tubewells contaminated. The assumption is that all tubewells, contaminated or uncontaminated, have equal number of users under each category. It may be observed that shallow tubewell even at this level of contamination still providing water with arsenic within the acceptable level to about 75 million people in Bangladesh. However, these safe tubewells may turn into unsafe in future.
 
 
 
 

Similarly, population exposed to different levels of arsenic from drinking water has been computed and presented in Figure 2.7.

Fig. 2.7. Population Exposed to Different Levels of Arsenic in Drinking Water

Department of Public Health Engineering, British Geological Survey and Mott MacDonald Ltd (MML) in Phase-1 studies estimated that the population exposed to arsenic contamination would lie in the range 18.5 – 22.7 million ( DPHE, BGS, and MML , 1999). However, The BGS-DPHE studies finally gave two estimates of population exposure based on projected population of 125.5 million in 1999 (BGS and DPHE, 2001). The estimates of total population exposed to As concentration above 50 and 10 m g/L using the kriging method were 35.2 million and 56.7 million respectively. Based on upazila statistics the exposure levels to As exceeding 50 and 10 m g/Lwere 28.1 million and 46.4 million respectively. School of Environmental Studies, Jadavpur University (SOES, JU), Calcutta and Dhaka Community Hospital (DCH), Dhaka estimated that the populations exposed to above 0.01 mg/l and 0.05 mg/l in 43 districts in Bangladesh were 51 million and 25 million respectively (SOES and DCH, 2000).

2.3.3 Estimated Risk

Arsenic is an ubiquitous micro-pollutant and naturally found in atmospheric air at concentration levels about 0.4 to 30 ng/m³, in food at concentration levels about 0.4 to 120 m g/kg, in soil at 5 to 6 mg/kg and in water at concentration levels from undetectable and up to few m g/L. Thus human all over the world is naturally exposed to small amount of arsenic. Arsenic is said to be essential for some animal species but not for human. Since arsenic is toxic and carcinogenic, ingestion of any amount of arsenic poses a risk

The commonly reported symptoms of chronic arsenic exposures are melanosis (hyperpigmentation, depigmentation etc.), keratosis, Gangrene, peripheral vascular disorder, skin cancer and a number of internal cancers. The most commonly manifested disease in Bangladesh so far is skin lesions. There is no well-established relationship between ingestion of arsenic through drinking water and its health effects. However, the multistage model developed by United States Environmental Protection Agency (EPA, 1988) based on the increased incidence of skin cancer associated with ingestion of arsenic in drinking water indicates that the concentration associated with an estimated excess lifetime skin cancer risk of 10^-5 is 0.17 m g/L. It is practically difficult to detect and measure arsenic at 0.17 m g/L concentration in water by any technique. Considering this difficulty, WHO in 1993 made a provisional guideline value of 10 m g/L for arsenic in drinking water, which is associated with a lifetime excess skin cancer risk of about 6 per 10,000 population. The Bangladesh Standard of 50 m g/L is associated with a higher risk of 30 per 10,000 population. However in an area or in a country, the people using different sources of water are not exposed to equal concentration of arsenic as shown in Figure 2.6. Using the EPA model and distribution of population exposed to different level of arsenic, the estimated total numbers excess skin cancer risk under different conditions of water supply for the present population of 129.25 million in Bangladesh are given in Table 2.4.

Table 2.4 : Estimated Incidences of Excess Lifetime Skin Cancer in Bangladesh