Economic Cost-Benefit Analysis of Rainwater Harvesting Systems in Coastal Bangladesh: A Case Study of Mongla Upazila

Abstract

Coastal communities in Bangladesh face increasing challenges in securing safe and affordable drinking water due to salinity intrusion, erratic rainfall, and reliance on costly alternative water sources. This study evaluates the economic viability of household-based Rainwater Harvesting (RWH) systems in Mongla, a salinity-prone upazila in Bagerhat district. The primary objective is to assess whether investing in RWH infrastructure is a financially sound solution for households facing water scarcity and related health burdens. Using a Cost-Benefit Analysis (CBA) framework, the study calculates key financial indicators including Net Present Value (NPV), Benefit-Cost Ratio (BCR), Internal Rate of Return (IRR), and Payback Period over a 20-year project lifespan. Real-world data from 100 RWH users and 100 non-users were collected through surveys, incorporating capital, operational, health, and time opportunity costs. Findings indicate that RWH adoption results in an NPV of 293938.6 BDT, a BCR of 20.9, and an IRR of 236.09%, with a payback period of less than one year. Additionally, RWH systems substantially reduce the time and medical costs associated with water collection and waterborne diseases. Sensitivity analyses confirm the system's resilience under fluctuating cost and benefit scenarios. These results strongly support RWH as a cost-effective and scalable solution to address drinking water insecurity in coastal Bangladesh. The study recommends policy integration of RWH into national water strategies, financial incentives for low-income households, and technical training for system maintenance to enhance community-level resilience and sustainable water access.