Rainwater can be an irrigation lifeline

Every monsoon, Bangladesh receives around 2,500 mm of rainfall, but much of this rainwater flows into rivers and drains without being captured. Meanwhile, farmers face water scarcity during the dry season and groundwater levels in cities, including Dhaka, have declined sharply due to over-extraction for irrigation. Amidst climate change threats and increasing salinity, rainwater harvesting is emerging as a practical solution to support irrigation, safeguard food security, and build resilience.

Groundwater extraction in Bangladesh is among the world's highest, with over 90 percent of groundwater used for irrigation. In Dhaka, water tables have dropped by 60-75 metres, while in the north, depletion threatens agriculture and drinking water supplies. Without intervention, groundwater scarcity will intensify by 2030, risking land subsidence and a decline in crop productivity.

However, rainwater harvesting, a centuries-old practice, can offer a solution if modernised to collect, store, and use rainwater for irrigation during the dry season. In coastal districts like Satkhira and Khulna, where salinity restricts freshwater access, many households use storage tanks to collect rainwater. This allows them to cultivate vegetables and grow backyard gardens, thus improving nutrition and livelihoods. These low-cost systems have empowered women, who maintain water systems in their communities and earn additional income.

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Rainwater harvesting also aligns well with water-saving irrigation methods. The Alternate Wetting and Drying (AWD) technique, promoted by the Bangladesh Rice Research Institute (BRRI), International Rice Research Institute (IRRI), and Asian Development Bank (ADB), reduces water use while maintaining rice yields. Field trials in Naogaon and Sirajganj have shown that AWD can reduce water usage by up to 20 percent, lower irrigation costs, and cut greenhouse gas emissions by 30 percent without harming yields. Farmers have reported stable or even increased production while using fewer irrigation cycles, demonstrating how rainwater storage and water-efficient practices can complement each other for maximum impact.

Despite its clear benefits, the adoption of rainwater harvesting for irrigation remains limited. The Bangladesh Water Act, 2013 encourages water conservation but lacks clear incentives or subsidy mechanisms for farmers to install rainwater systems. Although the Bangladesh National Building Code (BNBC) mandates rainwater harvesting for all new buildings constructed on plots larger than 300 square metres, enforcement is weak, and retrofitting remains rare. There is also a lack of clear guidelines on how to implement farm-scale rainwater harvesting systems, making it harder for rural communities to adopt the practice systematically.

A 10,000-litre tank connected to a 150-square-metre rooftop can provide sufficient water for household and small-scale irrigation needs throughout the dry season. In rural areas, bunds and ponds can capture monsoon runoff for later use in fields, reducing dependence on groundwater. In urban industrial zones, factories are beginning to explore rooftop rainwater harvesting for non-potable industrial processes, which could significantly reduce their groundwater dependence while building climate resilience.

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Addressing the critical challenge to our water security

A clear, integrated policy approach to harness the full benefits of rainwater harvesting is needed. Subsidy programmes, tax incentives, and low-interest financing for rainwater systems would encourage farmers and industries to invest in them. Public-private partnerships can help scale up local tank production, and trained community-based maintenance teams can ensure that the systems remain operational and effective for years. Local governments can integrate rainwater harvesting with broader climate adaptation strategies to build resilient water systems at the community level.

Affordable modular tanks, gutter systems, basic filtration units, and low-pressure pumps can be assembled locally at manageable costs. Community-driven initiatives led by women's groups have shown how collective action can sustain rainwater systems, while private sector engagement can drive innovation in design and maintenance services.

Rainwater harvesting for irrigation also aligns with Bangladesh's climate commitments. By reducing groundwater extraction, rainwater harvesting helps conserve aquifers, while water-efficient farming methods like AWD reduce emissions. Consequently, smallholder farmers can lower production costs while improving productivity and resilience to weather shocks. As the climate crisis deepens, traditional reliance on groundwater will become increasingly unsustainable. In contrast, rainwater harvesting is a nature-based, practical, scalable, and equitable solution. With supportive policies, investments, and community engagement, Bangladesh can transform its monsoon rains into a year-round resource for agriculture, livelihoods, and climate resilience.

Dr Makhan Lal Dutta is an agricultural engineer, and chairman and CEO of Harvesting Knowledge Consultancy. He can be reached at [email protected].

Views expressed in this article are the author's own. 

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