**5.2 Cost analysis of RWH system**

The main objective of RWH is to decrease the usage of groundwater and provide both drinking water and non-potable water. The rain water usually contains various contaminants that has to be filtered and disinfected before being used for domestic purposes. Non potable usage of RWH includes gardening, washing and toilet purposes and so requires

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

#### **Figure 4.**

*Schematic diagram of rainwater harvesting scheme in Gosaba, South 24 Parganas.*

no treatment. The physical, chemical and biological treatment of harvested rainwater is not required that makes the RWH system economical and cost effective [1]. The storage tank is the costly part of the entire RWH system, the cost analysis presented here consists of cost of materials and construction of storage tank at Gosaba R. R. Institute, Bharat Institute of Information Technology, PRITET computer training institute, South 24 Parganas.

The details of the quantity of materials used for construction of reservoir is given in **Tables 4** and **5**.


#### **Table 4.** *Details of quantity.*


#### **Table 5.**

*Rate analysis of materials.*

For concrete work, Sand = (1/4 × 1.54 × 112.56) =43 m3 ; Stone chips = 86 m3 . For plastering, Volume of wet mortar = (20/1000 × 272) = 5.44 m3 . Dry volume of mortar = (5.44 × 1.3) = 7.07 m3 . Cement = (7.07/3) = 2.35 m3 ; Sand = 4.7 m3 . For PCC work, Cement = (20.29 × 1.54 × 1/13) = 2.40 m3 . Sand = 9.6 m3 ; Stone chips = 19.2 m3 .

## **6. Conclusion**

The present study assessed the suitability of rainwater harvesting and its use in various domestic and irrigation sectors in a very remote area of West Bengal having scarcity of good quality of water. Gosaba block of West Bengal is a very much water scarce area, as the groundwater in the location is contaminated with saltwater and arsenic. Therefore, there is scarcity of freshwater required for domestic works, irrigation and drinking purposes. In order to get rid of the problem and to maintain the GWT, an alternative method of harvesting rainwater is adopted for the present study. Rainwater harvesting is defined as the method of supplying fresh water in salinity and arsenic affected coastal areas of West Bengal. The availability of rainfall as runoff is estimated based on different empirical equations. The area received maximum rainfall in July–August of 2020 with a normal rainfall of 196 cm. To augment the supply of water to the ten thousand people in the study area, three institutional buildings are chosen. Water is collected at the roof catchment area of those institutional buildings. Through pipe and valve surplus, rainwater is conveyed to the rapid sand filter which is composed of sand, gravel and further carried to the reservoir to store and supply water throughout the year. Before distributing the water, chlorination is applied. By proper grid system and arrangement of boost, station water is supplied to every consumer at an affordable cost of installation of rainwater harvesting system. The tank has storing capacity of 70 l/capita/day of water ad total cost of project is just Rs 35,057,000 which is reasonable. It was also found that the quantity of stored and harvested rainwater could be used throughout the year and not only in rainy season.

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