**1. Introduction**

Various regions of West Bengal as well as India are facing the problem of water shortage due to depletion of groundwater table (GWT) at an alarming rate. South 24 Pargana located in the coastal area of West Bengal, India is one of them. Gosaba is one of the blocks in South 24 Pargana. The latitude and longitude of Gosaba are 22.16°N and 88.80°E respectively. The population density of South 24 Pargana is larger than that of West Bengal. Due to excessive use of groundwater, saline water intrusion is taking place

rapidly in South 24 Pargana. The groundwater of Gosaba is contaminated by arsenic and also affected by saline water intrusion from the Bay of Bengal. Thus, there is scarcity of freshwater required for domestic and drinking purposes in the Gosaba region. It is very much needed to provide fresh water to different sectors and most importantly for household purposes. Since during monsoon tropical regions receives heavy rainfall, rainwater can be stored for future. Therefore, as an alternative rainwater harvesting (RWH) can be adopted to provide fresh water to the household during dry seasons at a reasonable cost of installation or for recharging groundwater. There are three processes involved in RWH technique: collection of rainwater in a waterproof surface such as impervious ground surface or roof, conveying the water through pipes and conduits from catchment to suitable storage tanks and storing the water properly at some location, may be rooftop or underground tank for future use. It includes primary screening of unwanted materials, first flush diverters and a water treatment plant. The harvested rainwater can decrease the dependency on groundwater caused by increased rate of population. RWH techniques can also prevent soil erosion and flood in coastal areas during rainy season as the excess water is collected in huge tanks. Storage tanks made up of concrete are most widely used in India to store rainwater and can be built below and above the ground surface. Although it is advisable to provide tanks above the ground surface as it is cost- effective and any damage, leaks, cracks etc. can be easily identified and tanks could be cleaned at regular intervals. Moreover, there remains a risk of contamination of water in underground tanks.

Various researchers worked on the RWH techniques to reduce the scarcity of fresh water and save the groundwater. Awawdeh et al. [1] studied that the chronic water shortage in Jordan can be reduced by increasing the amount of rainfall harvesting from rooftops, roads, and parking lots. They conducted a study at Yarmouk University and evaluated the potentiality for potable and non-potable water savings by using rainwater [1]. Tobin et al. [2] studied the practice of rainwater harvesting (RWH) in a rural community in Edo State, Nigeria. A cross-sectional study design and a structured observational checklist were used for the assessment of the household rainwater harvesting system. Data were analyzed using statistical package for social sciences (SPSS) version 16 and results were presented as frequencies. It has been found that RWH was practiced by over 80% of households, with the rooftop as the catchment area. Stored water was most commonly used for personal hygiene purposes [2]. Roy [3] conducted an empirical study on the Bandu river basin in Puruliya district to explain the importance of rainwater harvesting in drought-prone areas of West Bengal. Puruliya district ranks first in vulnerability to drought hazards within the state of West Bengal. The Bandu river basin receives 1150 mm of rainfall even in the driest years but the distribution is uneven, as a resulting scarcity of water occurs. There are 31 villages in the Bandu river basin and the population density of the area is 375 persons/sq.k.m. The objective of the work was to adopt rainwater harvesting and estimate the runoff from the amount of rainfall received. The runoff was estimated through four empirical formulae and the results indicate the amount is a healthy one [3]. Khan [4] made a detailed review of the contribution of rainwater harvesting in the field of agriculture in the Ahmadabad region of Gujarat. Because of the little supply of water in villages by the government, the rural population is fully dependent on water for agricultural as well as domestic purposes. Both primary and secondary data from water samples and community surveys were used to analyze the costs and benefits of RH in the district. The major costs include the initial construction cost of the rainwater harvesting system and the maintenance costs. The major benefits include an increase in household dispensable income, time and energy saved

## *Analysis of Rainwater Harvesting Method for Supply of Potable Water: A Case Study of Gosaba… DOI: http://dx.doi.org/10.5772/intechopen.106537*

from collecting water, and relief from epidemic droughts [4]. Said [5] carried out a case study in South Delhi to assess the potential of roof-top rainwater harvesting procedure. The study aims to explain rooftop rainwater harvesting that can be easily used by each individual with ease. Data were collected and analyzed in relevance to the actual average annual water consumption of each household and the volume of rainwater collected annually from an individual respective rooftop. The study advised the reduction of 20% in the per capita demand of each individual. The present study finds its usefulness in developing awareness towards the proper use of rainwater for sustainable management of water resources at an individual level [5]. Shittu et al. [6] used a rainwater harvest system to combat perennial water scarcity at the household level in Ibadan city. They collected rainfall data for a period of 10 years. The RWH System used comprised of six basic components: Roof Catchment; Gutters and Downspout; Conveying and Water Treatment, Leaf Screen and Roof-washers; Storage Tanks [6]. Kulkarni [7] summarized studies, research and surveys carried out to study, analyze and implement RWH. It has been observed that the use of the RWH method can fulfill more than 50 percent of water demand in domestic households. The commercial hubs, school complexes, and office premises have more potential for rainwater harvesting [7]. Khan et al. [8] adopted a rainwater harvesting system for the design of optimum rainwater storage tank size and efficiency assessment. The software developed by them proved to be satisfactory for any combination of location, catchment area, material, and water demand and can also estimate the reliability of the corresponding water supply system. The rainfall data for a 24-year period for different areas of Bangladesh was collected from Bangladesh Meteorological Department (BMD) and used in the model. The software was employed to evaluate RWHS in an arsenic affected region (Comilla), coastal location (Khulna), and a low-rainfall area (Rajshahi) [8]. Jagtap and Bhosale [9] developed a working system at a construction site named Daulat Heights in Pune, Maharashtra. The main objective of this paper was to make efficient use of rainwater and adoption of the newly launched concept of nature conversion. The project has to store a capacity of 129,600 liters of water with just Rs 48,060 [9]. Pauline et al. [10] primarily focused on the adoption of water harvesting structures by farmers in dryland areas of Tamil Nadu. A thorough study was conducted and designed by combining a descriptive survey of the study area and a population analysis approach of a participatory study. Different water conservation methods/structures found in the dry areas of Tamil Nadu are farm ponds, tank irrigation systems; compartmental bunding and recharge pit, etc. have been described [10]. Chakraborty et al. [11] have simulated the GWT in various locations of Purba Medinipur with the help of Visual MODFLOW. The lowered GWT is one of the major reasons for salinity in groundwater in Purba Medinipur. From the review of literature, it is evident that RWH technique is advantageous and can be developed for both quantitative and qualitative approaches for the present study area [11]. Chowdhury et al. [12] conducted a comprehensive study in West Bengal and Assam that revealed that there is substantial amount of arsenic affected areas in these two states that is affecting the quality of groundwater and causing various diseases in human being. They also provided few suggestions to treat the arsenic sludge [12].

The present study aims at calculation of runoff available for storing during rainy season using two empirical equations derived by Aiexander Binnie; Ingels-De Souza and T.G. Barlow; determination of Ar content, Cl content, Fe content and salinity in groundwater of South 24 Pargana, designing and installation of RWH plants and explaining the economic benefits of RWH methods.
