Day 02::Thematic Session 04

Day 02::Thematic Session 04

Rainwater harvesting in arsenic prone areas

Bangladesh Convention on Rainwater Harvesting
Hotel Ruposhi Bangla, Dhaka
15 to 17 June 2012


The theme of this parallel session was ‘Rainwater harvesting in arsenic prone areas’. Arsenic contamination of water is a major concern for many regions in Bangladesh and this session specifically addressed this issue. The paper presenters were: Mr Mohammad Prottoy Khan, Mr Kazi Rashed Hyder, Mr Dipak Chandra Roy and Dr Md Rezaul Karim.

The whole session was moderated by the chairperson of the session Dr. Kazi Matin Ahmed and the panelist was Mr. Peter Ravenscroft

Following are the deliberations:

Paper 1: F Cubed Rain Water Collector and Carocell Solar Water Purifier by Mr Mohammad Prottoy Khan

F CUBED is an Australian owned, global company, dedicated to the conservation, production and processing of the world’s most critical resource, Water. F CUBED was established in 2004 to develop Solar Thermal Desalination, Zero Liquid Discharge (ZLD) and Solar Water Treatment Systems. The company has spent the past five years investing in research and development for a unique desalination unit powered entirely by the sun, to be known as Carocell. Carocell solar desalination/purification technology is the most efficient and cost effective product of its kind. Carocell solar panels can easily collect rainwater, so it functions as both a solar water purifier and a rain water collector.

• Qualities of Carocell:

– It produces pure clean potable water from any water source (including polluted industrial waste water, brackish groundwater, sea water and arsenic contaminated water)

– No green house gas emissions

– Zero liquid discharge

– Uses no chemicals, no membranes,

no electronics, no filters and no ongoing power source

• The objectives of the F Cubed Solar Water panels are that:

– It ensures safe rain water collection without any contamination.

– It is robust and can easily be moved from one place to another.

– Both safe rain and drinking water can be collected from the same device.

– It can desalinate sea water and can purify arsenic contaminated water.

– It has very low maintenance and operating cost.

F Cubed as a potential source of rainwater harvesting:

F Cubed Panel may also be used as a Rainwater Collector since the rain water collector can capture rainwater by means of the plastic film (1/2 inch Poly Carbon sheet) attached at the bottom of the panel. Rainwater can be collected in the same container as the distilled water or in a separate portable containers or larger tanks for storage. Panels will substitute the usage of roofs of houses for rainwater harvesting. Roof rainwater is not drinkable and requires treatment before consumption and may carry pollutants, such as animal and bird faeces, mosses and lichens, windblown dust, particulates from urban pollution, pesticides, etc. F Cubed Carocell panel can be easily reached and cleaned as it will be approximately only 5 feet off the ground. Whereas roof tops are difficult to clean because of height.

Concluding remarks:

Mr. Khan concluded his presentation by emphasizing that F Cubed Carocell Solar Water Panel is a unique product. It is a quantum leap forward in the use of direct solar energy to purify water and it can make a great contribution to Rainwater Harvesting. F Cubed Carocell Panels can work throughout the year as a rainwater collector mostly during rainy seasons and as a solar water purifier during dry seasons or as a combination of both. It can help to accomplish the overall purpose of providing safe and pure drinking water to the people without posing any harm to the environment.

Paper 2: Artificial aquifer -An adaptation of traditional rainwater harvesting systems Mr Kazi Rashed Hyder

Mr Hyder mentions his presentation that there are limited safe water sources in Bangladesh. The shallow aquifer is unsuitable, the deep aquifer is not available and the surface water polluted. Coastal areas face the threats of salinity intrusion, arsenic and iron contamination. Access to safe water is decreasing as surface water threatened. As a consequence increasing health problems, social problems and migration arise.

• The existing potable water facilities and their limitations:

– Shallow Tubewell

  • High Arsenic and Iron concentration
  • Saline water intrusion
  • 99% tubewells are non-functional

– Deep Tubewell

  • Lack of availability of deep aquifer
  • Saline intruded aquifer
  • 78% tube wells are non-functional

– Pond Sand Filter

  • Becoming saline intruded pond
  • Becoming dried up
  • Close observation and monitoring needed
  • Fresh water ponds not available

– Rainwater Harvesting System

  • Insects grow
  • Insufficient catchments areas
  • Not having round the year
  • Existing interventions are non-functional

Therefore, utilizing rainwater is the only safe and feasible alternative for the people who are affected by the shortcomings of the above mentioned methods. An artificial aquifer should be used for rainwater storage. This is basically an underground tank which is filled with filter media (fine sand, coarse sand and coarse aggregate). It is a round cylindrical shape with tube well pump head and platform. It varies greatly in size and is lined with masonry or Ferro-cement to several thousand cubic metres. Small tanks are lined with clay or geo-membranes. A geo-textile layer can be used as membrane for obstructing silt or clay into the filter media.

Consideration for construction: Slope of Catchment Area,Tank lining, Filter Media, Turfing, Pump Head

• Advantages of this method:

– Easy availability of drinking

– Can serve at water scarce areas

– Reduces social harassments

– Reduces water borne diseases

– Cost effective and sustainable

– Made of locally available materials

– User friendly technology

• Disadvantages

– Change of Rainfall pattern

– Reduction of infiltration rate

– Close O&M of catchments

– Clogging of filter media

– Could not be served over the designed/ estimated beneficiaries during dry season

– Practical field test is required

The Moderator thanks Mr. Hyder for his presentation and opened the floor for questions addressed to the two presenters from the audience.

Open discussion:

Questions addressed to Mohammad Prottoy Khan and his answers:

1. What are the economic aspects of Carocell? How much will 1 liter cost to be purified?

Answer: One Carocell panel costs USD 300. It has been estimated that 1 liter of water will amount to 7 paisa. WASA charges more than 7 paisa. Rainwater will be unlimited.

2. How much water is collected per day? Is it feasible for a large family?

Answer: Carocell will produce 20 liters of water per day, and rainwater can be collected all day if it rains all day.

3. Can the same panel remove arsenic and salinity?

Answer: Yes, the same panel has dual functions.

4. Can the solar panel desalinate water on rainy days?

Answer: The solar panel cannot desalinate water without the sun

5. Pure distilled water is very harmful for health since certain minerals are definitely needed. Then how can you declare that your product is suitable for health?

Answer: F Cubed as carried out a research which has proved that pure distilled water is not harmful.

Questions addressed to Mr. Kazi Rashed Hyder and his answers:

1. Catchment area for the artificial aquifer must be restricted, but isn’t that a big disadvantage for large populations and were the area is less?

Answer: Catchment area can used as playground but not as grazing field.

2. How can a catchment area be created in plain fields?

Answer: The slope must be made during the time of the construction of the catchment in plain fields, high grounds should also be chosen.

3. You mentioned that 78% of tube wells in coastal areas are non-functional, why is that?

Answer: Due to a lack of a deeper aquifer and salinity intrusion, the tube wells are non-functional.

4. Is there any real evidence of insects in water tanks?

Answer: Different organizations say that insects do not breed in water chambers. But our research has proved that without a filtration system, insects do breed in water chambers.

Paper 3: Rain Water Harvesting Technology: A learning from Practical Action, Bangladesh by Mr Dipak Chandra Roy

The presentation by Mr Roy mainly focuses the research results of the project carried out by Practical Action in Sathkhira. RWH is a feasible option since Arsenic contamination is a major concern in Bangladesh. As he reveals some data as 28. 9 % tube wells have arsenic as of 2009, 2 crore and 20 lacs people have no source of arsenic free water, 7crore 70 lacs people are in arsenic risk and Arsenicosis patient in Bangladesh was 56758 as of 2010. Water scarcity in certain areas (hard to reach, hilly area), depletion of ground water and availability of rain in Bangladesh are factors which encourage the use of RWH. Besides, the National Policy for Safer Drinking Water and Sanitation 1998, the National Arsenic Mitigation and Implementation Policy 2004 and the Draft Water Act 2012 all support the use of RWH.

Mr Roy shows some model of rainwater harvesting in his presentation. Out of these, Model 4 is the most suitable because:

– Suitable in case of absence of ideal catchment

– Outside the homestead where space is limited, easy operation and maintenance

– It is suitable wherever the roof is used as machha (local name) for vegetable cultivation, less chance of contamination

– Avoid cutting of branches and trees hanging over the roof, Water quality good

Design Considerations for these models:

– Local rainfall data and weather pattern

– Roof (or other) collection area / Catchment’s Area

– Roof type (Metal sheet/Tiles/Thatch/Golpata/Asbestos)

– Runoff coefficient (this varies between 0.5 and 0.9 depending on roof material and slope)

– User numbers and consumption rate (As purpose of use)

– Construction Material Cost

Mr Roy tips for field implementation, training to masons on construction and operation and maintenance, basic training to beneficiaries on operation and maintenance and refresher training was needed.

Paper 4: Safe and Sustainable Rainwater Harvesting in the Coastal and Arsenic Affected Areas of Bangladesh by Dr. Md. Rezaul Karim

Giving an introduction of the coastal area of Bangladesh Mr Karim says, pond sand filter, Rain-feed pond water and rainwater harvesting are the commonly used water supply options in the coastal areas. Since rainfall in the coastal areas is much higher than the average rainfall, RWH is a good potential water supply option of drinking and cooking water in the coastal areas.

Due to Arsenic in the shallow aquifer the rural water supply coverage has reduced from 97% to 74%. Providing safe, arsenic free, potable water to the arsenic affected areas is the most difficult challenge for the water supply sector of the country. In the National Policy for Arsenic Mitigation –

Potential Options are:

– Rainwater Harvesting (RWH)

– Pond Sand Filter (PSF)

– Deep Tube well

– Pipe Water Supply

Among the options, RWH is considered the most suitable option of providing safe water to the arsenic affected communities in Bangladesh. Mr Karim points some chart from the studies conducted by him and shows excess rainwater in monsoon may be stored for use in dry season.

• A total of 1000 rooftop RWH systems were investigated: 14.8% – community based and 85.2% – household based systems. Community based RWH systems were mainly school-based systems with Reservoirs capacity > 50,000 L and made of RCC or ferrocement. Household based RWH systems are made of ferrocement, plastic or RCC and the capacity ranged from 500 L to 3200 L

• For Household RWH, reservoirs of 2000L and 3200L capacities are found to use commonly. Community based reservoirs had a capacity of more than 10,000 L. The cost of 2000L capacity fibrocement tank ranges from Tk. 5,000 to 6,000 and is suitable for a family of 5 to 7 members. The cost of 3200L ranges from Tk. 7,000 to 8,000 and suitable for 9 to 10 members. About 91.9% of the RWH systems are in operation and are used for water collecting for drinking and cooking. For the community based RWH systems, the roof catchments are mainly RCC (41.2%) and CI sheet (58.8%). The household RWH systems consisted of CI sheet (about 73.9%) and few are RCC (about 8.0%).

Conclusions drawn from the samplings:

– The quality of the HRW depends on the materials of the storage reservoirs.

– Physical water quality like color, turbidity of most of the water samples were well below the Bangladesh Drinking Water Quality Standard (ECR, 1997) and WHO Guideline (2004) and water is aesthetically acceptable to the consumers.

– Among the chemical water quality parameters, only pH of water exceeded the maximum recommended value of 8.5. pH of the water depends on storage tank materials.

– The distribution of water pH follows as: pH (plastic) < pH (brick) < pH (RCC) < pH

– storage reservoirs must be done at least once in a year before the monsoon

– International and national organizations must take an active interest in this method of water collection

With these remarks and suggestions, Moderator invites the audience for open discussion

Open discussion:

1. Is the Model that he has supported in his presentation economically feasible?

Answer: The average cost of this model is BDT 12000. This may not be affordable for the poor, nut if the benefits are calculated then it should be considered feasible.

2. Use of PBC tanks are more feasible than the costly ones suggested, then why weren’t PBC tanks used for storage?

Answer: Several options were explored, around 12 different samples of storage containers were tested- from the ‘motka’ to the more expensive materials. It was found that the longevity of PBC was less than brick tanks, since they were prone to heat and could not store water for large periods of time.

3. Ferro cement has high levels of pH as your tests show. Why is that? What are the alternative options to ferro cement?

Answer: In ferro cement tanks, the pH level goes beyond 11 in some rare cases. But mostly the pH goes beyond 8.5 due to leaching into the water from the ferrocement. At the initial stage, the pH increases but after about 1 year, the pH level becomes normal.

4. The low mineral content in water may cause harm, in that case what are the alternative?

Answer: Minerals may also be supplemented by food intake, but in dire cases, there are no better options for many other than drinking rainwater.

5. How will these RWH be maintained after organizations have assisted in building them?

Answer: Communities should have a committee trained by NGOs to maintain the storage facilities.

The Chairperson and Moderator then ended the question-answer and requested the hon’ble panelist, Mr. Peter Ravenscroft to say a few words.

Mr. Peter Ravenscroft

Water Supply Specialist, UNICEF

The issue which is more threatening than water containing arsenic is: no water at all. There has been a lot of debate in this session of whether rainwater is pure distilled water or not. The best solution to resolving this problem is to add distilled water to a little ground water which will then cause the pH level to return to normal.

F Cubed has brought forward a new and original concept. However, a commercial product must be treated cautiously. Some important questions must be asked regarding it, such as: Does it really work? Is it safe from a bacteriological point of view? Is it acceptable to the rural people? Is it a viable solution for the millions of rural people? Independent people must be involved to assess this product.

The WHO must be consulted regarding the maintenance of the catchment area of the RHS and water maintenance.

Two conventional methods of RWH have been presented in this session, however, Mr. Karim did not explore the area of operation and maintenance fully and Mr. Roy should have carried out several different water bodies to sow their content.

The cost, level of service, health standards are all important factors of a RWH.

His last recommendation was that the evidence base must be made stronger using solid proof if such a concept as RWH is to be promoted.


Dr. Kazi Matin Ahmed emphasized that ‘Safe Water’ is the main message of this conference- the source, whether ground water or rainwater is not the factor. Whatever source is used, it must continuously monitor and the safety must be ensured.

The decline or drop in water levels is always sit-specific and does not apply to the entire country-therefore regional initiatives must also take place.