1. Water Distribution Network Systems

The solar-powered safe water system has been established by NGO Forum in di­fferent settings to supply safe, clean drinking water to Rohingya refugees living at Cox’s Bazar. The improved water networks are completely solar powered with green and non-polluting technologies in order to reduce energy costs and fuel emissions. The safe water systems run entirely on electricity which is generated through solar panels. Motorized pumps draw water from newly-installed two 95,000 liters, one 30,000 liters, one 20,000 liters and one 10,000 liters chlorinated water tanks which ensured to provide at least 20 liters of safe and clean water to every single refugee on a daily basis. Chlorinating water helps in maintaining safe water and eliminates any risk of the spread of diseases. Then the water is supplied to collective taps strategically installed throughout the blocks. These new systems improved the daily supply of safe, clean drinking water.

2. Surface Water Treatment Plant

Surface water treatment plant through Solar system A prospective option for development of surface water-based water supply system is the construction of community type Slow Sand Filters system. The technology with very high efficiency in turbidity and bacterial removal. It has received preference as an alternative water supply system for medium size settlements in arsenic and saline affected areas. In this very simple process, raw water from pond is pumped up from a pond; the turbidity gets down through the roughing filter and then discharged into the filtration unit. The water is filtered and then collected in a clear water reservoir by an under-drainage system. The main precondition is to preserve pond water from any sorts of external pollution or contamination.

A surface water treatment plant has been constructed which treated water through the Reverse Osmosis (RO) treatment process. In the reporting period, 3 treatment plants have been installed in di­erent capacities of 30,000 liters, 20,000 liters and 10,000 liters which cover a total of 1337 population. NGO Forum also conducted the water quality testing on a regular basis including FRC, pH, Cl, DO, TDS, Salinity, Resistivity, and Electrical Conductivity to ensure the quality of the water.

3. Rain-water Harvesting System

Rainwater Harvesting System is something that simply collects the rain which falls onto roofs, then stores it in a tank on over ground or underground and ensures uses over the year round.  Rainwater harvesting system has 3 basic units, the catchment area (like corrugated roof top), supporting collection system (gutter and collection pipe) and Storage tank, made of ferro-cement, burned clay (motka), brick wall etc. The collection pipe has an exit way beyond the connection with storage tank to let the first flush flow away. The down pipe has net to bar mosquitoes, flies and dirt from entering into the storage tank. There is an end plug to stop flush discharge to enter water into the storage tank after flushing. In many rainwater harvesting system an additional filtration unit is added on the top of the tank to ensure bacteria free water, sourced from catchment area.

4. Pond Sand Filter ( Slow Sand Filter)

A prospective and low-cost option for development of surface water-based water supply system is the construction of community type Slow Sand Filters commonly known as PSF. The PSF is a low-cost technology with high efficiency in turbidity and bacterial removal. It has received preference as an alternative water supply system for medium size settlements in arsenic affected areas. In this very simple process, raw water from pond is pumped up from a pond; the turbidity gets down through the roughing filter and then discharged into the filtration unit. The water is filtered and then collected in a clear water reservoir by an under-drainage system. The main precondition is to preserve pond water from any sorts of external pollution or contamination.

The horizontal roughing filter is divided into 3 parts: inlet tank, gravel zone and outlet tank. The gravel zone consists of 3 chambers loaded by different size of gravel (5-15 mm). The Sand Filter bed should be composed of 0.22 – 0.35 mm fine sand with a thickness of 60 to 120 cm. There is also a layer of coarse aggregate below the fine sand to support the sand against washing out through under drainage system. The uniformity coefficient of sand should be from 2 to 3, which is indicated as well sorted sand grains. The size of the gravel zone is 5-15 mm. On average the operating period of a PSF between cleaning is usually two months, after which the sand in the bed needs to be cleaned and replaced. Iron content exceeding 5 mg/l will require treatment using Iron Removal Unit (IRU). Dissolved iron in water is converted into insoluble ferric form in contact with air. This form will be removed by settling in the sedimentation tank and remaining by the filtration through sand filter.

5. Ring-well / Dug-well

The flow in a dug well is actuated by lowering of water table in the well due to withdrawal of water. The water of the dug well has been found to be free from dissolved arsenic and iron even in locations where shallow tubewells are contaminated. Dug wells are feasible in areas with stable soil layer at the top (a clay layer is preferable) and presence of sandy layer within 9 to 12 m.

For construction by manual digging, the wells should be at least 1.2 meters in diameter. Large diameter wells may be constructed for community water supplies. The depth of the well is dependent on the depth of the water table and its

6. Shallow Tubewell

Shallow hand tubewell (STW) is the most widely used low cost tube-well technology in Bangladesh that operates in suction mode. STW generally consists of no. 6 pump head with 38.0 mm (1.5 inch) diameter well pipes and filters. The foot valve and piston assembly are located into the pump head which is mounted at top of the ground level. This Suction Mode hand tubewell lift water by creating vacuum within the cylinder of the pump by raising the piston and allowing water to enter into the cylinder to fill-up the vacuum. This pump can lift water when groundwater table is within 7.5 m from the ground surface. Where aquifer formation consists of very fine sand, artificial sand packing is required around the screen of the tubewell which is called shrouding or gravel packing that increases the yield of the tubewell and prevents entry of fine sand into the screen.

7. Deep Tubewell/ Deep-set Pump

Deep hand tubewell (DTW) also operates in suction mode to withdraw groundwater from the deep aquifer where potentiometric surface of groundwater table exists within 7.5 m below ground surface. The deep aquifer is separated from the overlying aquifers generally by one or more impermeable or leaky permeable clay layers of varied thickness. The depths of the deep aquifers are generally more than 250 in the basin part. This water bearing zone comprises with medium to coarse sand in places inter-bedded with fine sand, silt and clay.

The term of deep aquifer is used in a number of ways depending on the target of its use. Considering geology and hydro-stratigraphy, it may be defined as deeper aquifer (Holocene/Late Pleistocene) separated by impermeable or leaky clay/silty clay layer from the upper aquifers. The depth of deep aquifers varies depending on geology and depositional environment of the sediment. Where the deep aquifer is separated from the shallow aquifer by substantially thick (>10m) impervious layer, the aquifer water can sustainably be drawn for drinking purpose. The deep aquifers in Bangladesh have been found to be relatively free from arsenic contamination and in coastal belt generally safe from salinity too. DTW were selected in areas where deep aquifer is separated from arsenic contaminated and saline affected upper aquifers by substantially thick impervious layer. The annular space of the vertically straight bore holes of the DTWs were sealed at the level of impermeable strata.

8. Piped water supply: Piped water supply system is running water supply system in rural Bangladesh using both STW and DTW as well as treated pond water for clustered rural settlements. In respect of convenience in collection and use, only piped water can compete with existing system of tubewell water supply. Good numbers of standposts with water delivery taps are connected for group of households upto kilometer distances.

9. Arsenic iron removal plant: Arsenic-iron removal plants (AIRP) is a relatively inexpensive way of removing/reducing arsenic content from groundwater for access to safer drinking water. Different options are provisionally certified by Bangladesh Council of Scientific and Industrial Research (BCSIR) of which most are household basis and one is community based. These can be selected as an ultimate option particularly where tubewell and Dug well is not feasible. Filter media needs to be changed after the media being clogged.

Chemical processes that may influence AIRP performance are iron and arsenic oxidation, arsenic co-precipitation with iron, multiple iron additions, interference by organics, and iron crystallization. Overall, AIRPs were shown to possess considerable promise for use in areas with high natural iron where users are concerned about arsenic and iron in their drinking water. However the performance of AIRP is influenced by arsenic speciation, oxidant type, point of oxidant application etc.

Dual platform tubewell both STW and DTW are useful in flood-prone areas for using water options in the dry and flood seasons as well as ensuring supply during heavy flood. One platform is constructed about 1.0 to 1.5 m high which is thus free from flood threats and can be used during flood seasons and another platform is at homestead land level which is being used in the dry season. An elbow pipe has been connected from the main boring pipe of the lower platform to the higher platform. This is thus an innovative system for the char, flood plain and low elevated coastal plain areas and highly context specific. During flood seasons, the head of the tubewell will be set with the pipe of high platform to keep the tubewell free from flood water and surface pollutants. This technology is also useful for coastal areas to protect quality of water during storm surges and waterlogged haor areas.

10. Desalinization plant: In the late 1960s, reverse osmosis (RO) was developed for desalting saline water supplies. This process is based on the principal of osmosis and requires a membrane barrier to separate salts from water. Because RO technology required considerably less energy to operate than distillation, it is considered to be the technology that would make desalination much more attainable to the world’s saline prone water scarce areas.

Desalination by RO requires the use of an osmotic membrane (allows water to pass through it at much higher rates than dissolved salts). Osmotic membranes occur naturally in living organisms everywhere. The osmotic membrane also is referred to as a semi-permeable membrane because of its capability to allow some constituents to pass through it while holding back others. In the RO desalination process, a pressure greater than the osmotic pressure applied to the saline water will cause fresh water to flow through the membrane while holding back the salts.

Saline water can be drawn from a surface water supply, a beach header-lateral face well system or a tubewell. Typically, groundwater is preferred because it provides a low turbidity feedwater requiring less pretreatment. Shallow groundwater of the coastal belt with moderate salinity concentration (EC 5000-6000 µS/cm) are using as raw water for desalinization plants.

Artificial recharge: Managed Aquifer Recharge (MAR) i.e. the augmentation of infiltration of treated safe and fresh surface water and harvested rain water into groundwater by different technologies is useful for aquifers subject to declining water levels, salinity encroachment etc. To meet-up the food security of huge population, Bangladesh became the world’s fourth biggest rice-producing country (Scott and Sharma, 2009 and IRRI, 2010), but unavailability of adequate water is a common phenomenon in the north-western part of the country mainly during dry period. The agro-based drought-prone north-western part of Bangladesh is well-known as ‘Barind Area’ dominated by uplifted Pleistocene Terraces. To support the irrigation demand, use of groundwater has been increased since years. At the same time the hydrogeological complexity, meteorological variability and climatic factors influence to increase the stress on this resource significantly. To combat the situation and explore the potential of MAR, a pilot project was undertaken in the Barind area installing recharge wells and using rainwater as source of recharge water. The study considered assessment of aquifer condition, groundwater quality, water level trend and recharge potentiality using primary and secondary data. In the study area, permanent lowering of ground water table was observed due to excessive withdrawal of groundwater in comparison to inadequate groundwater recharge during dry irrigation period. After application of MAR technique, ground water table started to raise in monsoon above the minimum depth to water table of previous years with the impact of artificial recharge. Therefore, the MAR, as an artificial groundwater recharge process, can be used as the potential groundwater recharge through rainwater in the drought prone area to improve groundwater conditions. Authorization for MAR should be granted only if the hydro-geological situation environmental condition and the recharge-water quality permit injection, percolation or infiltration of water taking into account all other relevant aspects, including ecological ones.