Water Use and Irrigation in Global Agriculture

Agriculture accounts for roughly 70 percent of all freshwater withdrawals globally, according to the UN Food and Agriculture Organization (FAO). That single figure reframes almost every conversation about water scarcity, drought resilience, and food security at once. This page covers how irrigation systems work across different farming contexts, where the major tradeoffs emerge, and what distinguishes a well-matched irrigation strategy from one that quietly drains an aquifer.

Definition and scope

Irrigation is the deliberate application of water to crops beyond what rainfall provides — a practice that has shaped global food supply chains for millennia and now underpins roughly 40 percent of global food production on just 20 percent of cultivated land, as documented by the FAO's AQUASTAT database (FAO AQUASTAT).

The scope matters: irrigated agriculture is not uniformly distributed. South Asia and East Asia account for the largest share of irrigated area, with India alone operating approximately 68 million hectares of equipped irrigation infrastructure (FAO AQUASTAT). In the United States, the 17 western states use the majority of the nation's irrigation water, a structural reality driven by the arid geography west of the 100th meridian. The USDA's National Agricultural Statistics Service (NASS Farm and Ranch Irrigation Survey) tracks irrigated acreage at the state level, offering the clearest picture of where and how American farms draw their water.

Water for irrigation comes from three main sources: surface water (rivers, lakes, reservoirs), groundwater (aquifers accessed by wells), and treated or reclaimed wastewater — a growing category in water-stressed regions. Each source carries different reliability profiles, regulatory frameworks, and long-term sustainability questions.

How it works

The mechanics of irrigation split into four principal system types, each with distinct efficiency characteristics:

  1. Flood (surface) irrigation — Water flows across the entire field by gravity. It is the oldest and most widespread method globally, but application efficiency typically falls between 40 and 60 percent, meaning a substantial share of applied water is lost to evaporation, runoff, or deep percolation before reaching plant roots.

  2. Sprinkler irrigation — Water is pumped through pipes and distributed via rotating or fixed heads. Efficiency ranges from 70 to 85 percent under good management conditions. Center-pivot systems, common across the Great Plains, are the defining visual of this category.

  3. Drip (micro) irrigation — Water is delivered directly to the root zone through emitters. Properly managed drip systems achieve efficiencies above 90 percent and reduce both water loss and the incidence of foliar disease. California's specialty crop sector — almonds, grapes, strawberries — relies heavily on drip infrastructure.

  4. Subsurface drip irrigation (SDI) — A variation where emitter lines are buried below the soil surface, nearly eliminating surface evaporation and allowing field operations to continue uninterrupted during irrigation events.

The efficiency gap between flood and drip irrigation is not merely academic. On a field of 500 acres under flood irrigation operating at 50 percent efficiency, converting to drip at 90 percent efficiency can theoretically halve consumptive water use — a meaningful number when aquifer levels are declining.

Scheduling is as important as system type. Irrigation timing based on evapotranspiration (ET) data — the combined rate at which water moves from soil and plant surfaces into the atmosphere — allows managers to replace only the moisture crops have actually used. The California Irrigation Management Information System (CIMIS), operated by the California Department of Water Resources, provides real-time ET data across hundreds of weather stations and represents one of the most sophisticated publicly available irrigation scheduling tools in the world.

Common scenarios

The practical application of irrigation plays out differently depending on crop type, climate, and water source:

Decision boundaries

Choosing an irrigation strategy involves navigating tradeoffs that do not always resolve neatly:

Efficiency versus capital cost: Drip systems outperform flood irrigation on water use, but installation costs can exceed $1,000 per acre for permanent crops. For smallholders or lower-margin commodities, the payback period may be prohibitive without subsidy support from programs like those administered through USDA programs and resources.

Groundwater versus surface water: Surface water rights are often legally senior and more visible to regulators; groundwater has historically been less monitored but is now subject to increasing state-level oversight. The balance between the two sources shapes farm risk profiles in ways that are easy to underestimate in wet years.

Crop match: Irrigation infrastructure should match crop water demand curves, not just peak-season availability. A well-designed system for wheat is structurally different from one engineered for tomatoes, even on adjacent fields. The broader resource base at the global agriculture overview offers context on how crop mix decisions interact with water availability at regional scales.

Climate trajectory: Long-range irrigation planning now incorporates projections on how precipitation patterns may shift — a dimension explored in depth on the climate change and crop yields reference page. A system sized for historical rainfall patterns in a given watershed may be undersized or mismatched within a single generation of infrastructure.

The core tension in irrigation management is that efficiency improvements do not automatically reduce total water consumption at the system level. When drip irrigation makes farming more profitable, it often incentivizes expansion of irrigated acreage — a rebound effect documented in the referenced literature and recognized by the USGS Water Resources Mission Area. Getting the accounting right — field-level efficiency versus basin-level consumption — is where irrigation science and water policy most productively collide.

References

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