By 2050, nearly half of the world’s urban population will face water scarcity — roughly 1.7 to 2.4 billion people unable to meet their basic water needs. That projection comes from a 2021 Nature Communications study that quantified the scope of the problem across four climate and socioeconomic scenarios. The headline is stark: the number of large cities exposed to water shortages will grow from 193 today to between 193 and 284 by mid-century, with India alone seeing a potential increase of 153 to 422 million water-scarce urban residents. India isn’t alone. Cities from Cape Town to Mexico City to Delhi have already rationed water during drought cycles, signaling that the future is already arriving in pockets around the world.
The Infrastructure Response — And Its Limits
Most cities have traditionally responded to water scarcity through what you might call “hard” infrastructure: dams to capture water during wet periods, desalination plants to convert seawater, and pipelines to move water from where it exists to where it’s needed. These approaches can work, but the Nature study offers a crucial insight: more than two-thirds of water-scarce cities can solve the problem through infrastructure investment. That “can” matters. It acknowledges both the potential and the catch: large-scale water solutions often carry environmental trade-offs that deserve careful attention.
Desalination requires enormous energy inputs. Dams flood ecosystems and displace populations. Long-distance pipelines represent capital-intensive, geographically specific solutions that don’t apply equally everywhere. What’s missing from this picture is a distributed approach — technologies and practices that work at neighborhood or municipal scale, that produce co-benefits beyond just water management, and that don’t require waiting for new mega-infrastructure.
The Digester as Water Recycler
This is where anaerobic digestion enters the conversation — not as a water treatment technology, but as a water recycling system embedded in waste management. Here’s how it works: food waste, yard waste, and other organic materials get digested anaerobically, producing biogas (which gets used for energy) and a nutrient-rich digestate byproduct. That digestate — a wet, semi-solid material teeming with nitrogen, phosphorus, and organic matter — gets applied to land as a soil amendment.
This is where water conservation quietly happens. Healthy soil amended with organic matter retains water more effectively. When liquid digestate is applied to landscapes, gardens, or agricultural land, it reintroduces water back into the hydrological cycle in a way that displaces demand for municipal freshwater supplies. A city that diverts its food and yard waste to local digesters isn’t just capturing energy and creating fertilizer — it’s also cycling water back into productive use, reducing its dependence on distant reservoirs or expensive desalination.
That’s a small but meaningful contribution to urban water resilience, especially when deployed at scale across dozens or hundreds of neighborhoods.
The Multiplier Effect
Water conservation is just one of the outputs. In the same digestion process, you’re capturing methane that would otherwise decompose in a landfill, converting it to usable energy. You’re diverting tons of material that would occupy limited landfill space. You’re producing digestate that reduces demand for synthetic fertilizers — which themselves require massive water inputs to manufacture.
For cities facing the water crisis described in the Nature study, the calculus is straightforward: every ton of organic waste that moves from landfill to digester is a ton that stops producing uncontrolled methane emissions, and every volume of liquid digestate applied to soil is water recycled rather than extracted. The solutions aren’t mutually exclusive. Dams, desalination, and digestion can coexist. But in a world where more than two-thirds of water-scarce cities need more than one tool in their toolkit, distributed systems like anaerobic digestion deserve a prominent role.
The urban water crisis is real and growing. But it doesn’t require waiting for a single silver-bullet technology. It requires layering many small solutions across the system — and digestion-based water recycling is already available to deploy.