The vegetables lining the shelves of Kannur’s bustling markets tell only half the story. Behind each onion, tomato, and cucumber lies an invisible flow of water—one that travels across state borders long before the produce reaches the consumer. A new study led by Anvar K. from the Centre for Water Resources Development and Management (affiliated with the University of Calicut) has mapped this hidden trade, revealing how water embedded in food moves from Karnataka, Maharashtra, and Tamil Nadu into Kerala, reshaping local water use and supply chain sustainability.
The research, published in *Water Science* (known in Malayalam as *Jalam Vijnanam*), quantifies the “virtual water” embedded in 78.48 tonnes of vegetables entering Kannur daily. The findings show that nearly 69% of these imports come from Karnataka alone, creating a silent hydrological bridge between India’s southern states. “Vegetables like onion and tomato dominate the trade, but it’s the less visible crops—like beans and ginger—that carry surprisingly high water footprints,” says Anvar. “This challenges the assumption that high-volume imports always mean high water use.”
The study breaks down water use into three components: green (rainwater consumed during growth), blue (irrigation from surface or groundwater), and grey (water needed to dilute pollutants from fertilizers and pesticides). The majority of the water footprint across most vegetables is green, reflecting rainfed farming in source regions. However, crops like cucumber and ginger show a significant blue water footprint, meaning they rely heavily on irrigation and could be straining local freshwater resources.
From a commercial perspective, this has implications beyond agriculture. Energy-intensive water pumping for irrigation in source regions—often powered by diesel or electricity—ties vegetable supply chains directly to the energy sector. As urban demand grows and interstate trade expands, the energy cost of virtual water could rise, especially in crops with high blue or grey footprints. “If cities like Kannur continue to rely on water-intensive crops from distant regions, they’re not just importing food—they’re importing water risk,” Anvar notes.
The study also highlights inefficiencies in sourcing. While onion and tomato dominate in volume, their water efficiency per kilogram may be lower than expected, and certain smaller-volume crops carry disproportionately high water costs. This suggests room for strategic sourcing—shifting toward lower-impact vegetables or supporting more efficient production regions.
For policymakers and businesses, the research underscores a growing need to integrate water footprint data into food trade and urban planning. As climate variability reduces rainfall predictability in rainfed systems, the stability of these virtual water flows—and the energy that powers them—could become less certain.
In a world where water is increasingly traded like a commodity, understanding these hidden flows is no longer optional. It’s a strategic imperative—one that connects the farmer’s field, the energy grid, and the dinner plate across hundreds of kilometers.