Rainwater Harvesting: An Alternative Source of Safe Drinking Water in Bangladesh

Research Article

Austin J Hydrol. 2014;1(2): 8.

Rainwater Harvesting: An Alternative Source of Safe Drinking Water in Bangladesh

Md. Manzurul Islam¹*, Chou FNF², Jyoti Prakash Maity³ and Kabir MR4

¹APS to Economic Advisor to the Hon’ble Prime Minister, Prime Minister’s Office, Dhaka, Bangladesh

²Department of Hydraulic and Ocean Engineering, National Cheng Kung University, Taiwan

³Department of Earth and Environmental Sciences, National Chung Cheng University, 168 University Road, Ming-Shung, Chiayi County 62102, Taiwan

4Department of Civil Engineering, University of Asia Pacific, Dhaka, Bangladesh

*Corresponding author: Md. Manzurul Islam, APS to Economic Advisor to the Hon’ble Prime Minister, Prime Minister’s Office, Dhaka, Bangladesh

Received: September 08, 2014; Accepted: November 13, 2014; Published: November 18, 2014


Groundwater has been reported to be contaminated by the Arsenic (As) since 1993, which was highly hazardous for human health and for food safety as well. The groundwater of 61 districts has been heavily contaminated by As. Thus, about 38,000 cases of arsenicosis were identified in Bangladesh. A lot of research works had been carried out to reduce the As-concentration at the acceptable limit. A lot of As removal technologies and options are available in Bangladesh. Almost all of those have technical and economic constraints to use by rural uneducated and poor people.

To overcome the As contaminated health hazards, rainwater harvesting was found to be one of the best remedial measures for the rural people of Bangladesh. A Yield Before Spillage (YBS) model using spreadsheet was developed for the study to optimize the rainwater storage tanks according to different numbers of family members ranging three to seven. It was found from the simulated results that different capacities tanks would be able to supply the required water demands of those different family members. The stored water could be used for drinking, cooking and dishwashing of a family throughout the year. The study found that the method to be very much potential.

Keywords: Rainwater harvesting; Arsenic mitigation option; Optimum tank volume; YBS


Groundwater is available in shallow aquifers in adequate quantity in the flood plains and Bangladesh achieved remarkable successes by providing drinking water at low-cost to the rural population through sinking of shallow tube wells. Unfortunately, As-contamination of shallow tube well water in excess of acceptable limit has become a major public health problem in Bangladesh. As-contamination of this groundwater has been reported from 1993 but in terms of severity, Bangladesh tops the list, followed by India and Vietnam in the world [1]. Hundreds of thousands of people in Bangladesh, daily use drinking water with As-concentrations several times higher than that of the World Health Organization (WHO) recommendation of 0.01 mg/L of water where as 0.05 mg/L for Bangladesh [2]. It was suspected that over 0.2 million people were suffering from As-related diseases, ranging from melanosis to skin cancer and gangrene. An estimated 35-40 million out of 130 million people are potentially at risk of As-poisoning from drinking water source in Bangladesh [3,4]. The lifetime excess risk (per 100,000 people) of mortality from liver, bladder and lung cancers attributed to arsenic in drinking-water were 198.3 for males and 53.8 for females, with an average across-gender lifetime risk of 126.1 [5].

During the last few years a wide range of small scale As removal technologies and options have been developed, field tested and used under action research programs in Bangladesh. Those technologies could be broadly categorized as: (i) oxidation and precipitation, (ii) coagulation and co-precipitation, (iii) sorption techniques and (iv) membrane techniques. The methods are not so easy to use in the rural areas of Bangladesh. Rainwater harvesting is an alternative source of safe drinking water and it is easy to use by the rural uneducated people of Bangladesh. Compared with the As removal methods, the quality of rainwater is better quality, the cost of construction and maintenance are low. Gomes [6] proved that rooftop rainwater harvesting systems for human consumption represent an alternative among individual technologies of water supply. A domestic rainwater harvesting system may be viewed acceptable from a technical (e.g. risk of demand not being met), economic (e.g. most economical tank capacity), or managerial (e.g. acceptable duration of time with empty tank) perspective [7,8] concluded that rainwater usage is economically feasible for most cases; and the higher the rainwater demand, the higher the feasibility. Parra et al. [9] reviewed that rainwater harvesting (RWH) systems can aid not only in meeting water demand partially, but also doing so in a more cost-effective and environmentally friendly manner than other techniques. The acceptance of the rainwater harvesting is better because some NGOs are now trying to establish it in some places of Bangladesh. The rainwater harvesting option can provide the people a maximum safety from As-contamination which is available in the rural area of Bangladesh. Islam [10] investigated that stored rainwater could be used up to four months as safe drinking purposes and if collected and stored properly, it could be used for longer period. If the rural people can store the rainwater at an air tight container, then the people may use it as drinking water for more than four months. It will reduce the risk of contamination. The objective of this study was to determine the capacity of rainwater harvesting tanks which could store rainwater and satisfy the demand throughout a year for a family having different members and it would help to promote the rainwater harvesting system as potential alternative water source to mitigate As-contamination.

For this study, a Yield Before Spillage model (spreadsheet) was developed for optimal tank size design. The study used to find the optimal sizes of the tank of a family having different family members. 10 years rainfall data (from 1996 to 2005) were analyzed and simulated to find the suitable data (minimum rainfall data) which was used in the simulation to determine the optimum tank capacities. The rainfall data is one of the very important parameters for the study. The rainfall pattern is changing with the climate change and this climate change scenario was also considered to find the suitable rainfall data. The model was simulated using different parameters like: minimum rainfall data, standard catchment area, water demands and storage tanks. Catchment area was considered as standard roof area of rural households. Water demands were considered for drinking, cooking and dishwashing purposes having different numbers of family members. After a lot of simulations, the study revealed the optimum tank sizes which could provide rainwater to a family throughout the year for drinking, cooking and dishwashing purposes.

Materials and Methods

Study area

Jhikargachha is an upazila (subdistrict) of Jessore District in the Division of Khulna, Bangladesh, was selected as study area for this research work. It is located at 23°6´0´N latitude and 89°7´59.88´E longitude. The land area of the upazila is about 308.09 km², total population is about 271,014 and literacy rate is 52% (BBS, 2007). It has 174 villages and about 58,391 households. This upazila is far away from the capital city (350 km). Average economic condition of the people of the study area is relatively poor. Culture of the people is mostly village oriented and professions of people are mostly agriculture. Households are mostly collective and communityoriented. Acceptance of any new technology or idea is less difficult; i.e. people are more open-minded.

Jhikargachha upazila was selected as study area because the biggest local NGO Bangladesh Rural Advancement Committee (BRAC) has been working in this area for a couple of years to mitigate the As problem and has already completed the testing of tube wells and the awareness level of the people. BRAC distributed different safe water options among the community as free demonstration units. These free options were located and distributed among people selected by the community itself. A limited number of options were distributed in each village, the intention being to motivate and raise the awareness of the villagers about the provided options. A small questionnaire survey was conducted to get the users perception about different options. Since the number of provided options in any one village was very low, perceptions of villagers about these options were collected from different parts of the study area.

Rainfall analysis

Bangladesh is a tropical country and it experiences heavy rainfall during the monsoon. Monsoon usually lasts from May to October and there is occasional rainfall also in November. Thus, during this period it gets ample rainwater, which could reduce the dependency on As-contaminated groundwater if it is harvested and stored properly. The rainfall in monsoon generally varies from 150 cm to 350 cm annually. Rainfall data collected from Jessore rainfall station from the year 1996 to 2005 (10 years) were analyzed and simulated for the study. Among these years, around 115 cm was found to be the lowest rainfall in year 2003 and used for the determination of the optimum tank size. This year’s data was also congruent with the average annual change ± 5% of the trend in annual precipitation from 1901 to 2005 which was determined by Working Group 1 of Intergovernmental Panel on Climate Change (IPCC AR4, 2007). IPCC determined average annual rainfall of 149 cm which is nearly equivalent to the study area’s minimum annual rainfall of that period. Thus, the annual rainfall used in the simulation to optimize the tank capacities for the study, was reasonable.

Demand analysis

The total per capita water demand for a family was very high. If rainwater harvesting system is considered to satisfy the total demand, then the storage capacity would be huge. The rainfall only lasts about five months in Bangladesh and for the rest dry period, the required storage volume would be very big and cost would be very high which would not be feasible for the rural poor people. On the other hand, it was found that As-toxicity mostly occurs through drinking water and contaminated food [11]. Considering these situations, only drinking, cooking food and dishwashing purposes were considered as demand for the study. The study area has different sizes of family members varying from three to seven or even more. But the survey study found that the majority of the families having five family members. This study has simulated considering different sizes family members like: three, four, five, six and seven. An average water requirement of 2 L/day/person for drinking purposes [12] was considered for the study area. According to the survey findings, the water demands for cooking and dishwashing purposes of the families having family members of 3,4,5,6 and 7 were assumed to be 16, 18, 20, 22 and 24 L/ day/family respectively for the study. These volumes seem to be very small compared to the standard water use rate, but these volumes were exclusively assumed for hardcore safe drinking water shortage area. The safe drinking water will be used only to clean the rice and vegetables and final washing the cooking pots. The meaning of dishwashing was to wash/clean the pots, plates and wash the hands before having foods.

Initial flushing device

Rainwater collects impurities and contaminants during flowing over the catchment, thus, it was necessary to have a first flush removal mechanism included in the system. During the dry period, dirt and bird droppings may seriously concession the quality of the collected rainwater. An automatic initial flushing device is shown in Figure 1 was designed and fabricated for the study to flush the roof or catchment. This device was developed to prevent the first rain from contaminating stored water with bird’s dropping, sediment and debris from the roof. To fabricate an automatic initial flushing device, a plastic pot (first flush water storage pot) having capacity of approximately 10 L (because it was determined that 6 to 10 L of water can clean the catchment), two PVC pipes (one is to collect first flush water and the other is to collect the clean water) of 30 cm length each, one lid which would close and open two inlets with the help of springs, two springs etc. were used. The device would work automatically. There were two inlets at the top of the device of which one carried first flush water and the other carried the clean water to the storage tank. The inlets would be closed and opened by one common lid on it with the help of two springs. Spring 1 would help to close the clean water inlet using the lid and it has less tension than spring 2. The first flush water collection inlet would be closed with the help of spring 2. If the lid opens the first flush water collection inlet, the clean water inlet would be closed by the lid simultaneously. Initially the clean water inlet would be closed and the first flush inlet would be opened. As the rain starts, the first flush water will store into the first flush water storage pot. When the water holding capacity will exceed the tension on spring 2, then it would pull the lid and would close inlet of the first flush inlet. On the other hand, the clean water inlet would open and store the clean water to the storage tank. When the rain would be stopped then the first flush water holding pot would be emptied manually by opening the stop cork. If the water from the first flush water storage pot is emptied, spring 1 will pull the lid and the clean water inlet would be closed automatically. The stop cork of the first flush water holding pot would be closed again to use it before starts the next rain.