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Neglected Blue Treasure: A Global Investigation into Brackish Water — An Invisible Water Source and Future Challenges in the Arid Age
2026-04-03
I. Global Distribution: A Hidden Giant Reservoir
1. Inland Salinization Zones
Brackish water is concentrated in arid and semi-arid inland closed basins, formed by long-term evaporation of marine and lacustrine sediments. In North America, southwest U.S. underground brackish water reserves are 35 times the country’s annual freshwater consumption, with 75% of New Mexico’s groundwater being brackish. In China, annual underground brackish water reserves exceed 60 billion cubic meters, 1/3 in Xinjiang (20 billion cubic meters), with 70% in southern Xinjiang. The Middle East and North Africa extract 5.1 billion cubic meters of brackish water annually in Algeria, 1.6 billion for drinking. Notably, southern Ningxia’s brackish water (mineralization >2g/L) totals 357.3 million cubic meters (29.5% of local water resources), but only 24 million cubic meters were used in 2020.
2. Coastal Intrusion Zones
Seawater intrusion, driven by sea level rise and over-extraction, is turning coastal freshwater aquifers brackish. In Asia, millions of wells in Bangladesh, Vietnam and India are undrinkable; China’s Bohai Rim, Yangtze and Pearl River Deltas face widespread shallow groundwater salinization. In the Americas, U.S. Gulf Coast and Florida aquifers are infiltrated, with New Orleans tap water turning salty. By 2050, all continental coasts (except Antarctica) will have a 1-kilometer-wide seawater intrusion zone.
3. Special Distribution
Two underutilized brackish water sources exist: offshore aquifers (U.S. East Coast, Hawaii, Australia’s northwest shelf) and high-altitude saltwater lake areas (Andean Plateau’s Lake Titicaca, Qinghai-Tibet Plateau), which gain value as these regions develop.
II. Water Quality Characteristics: Definition and Challenges
1. Scientific Definition
Brackish water is defined by total dissolved solids (TDS) of 1,000–10,000 mg/L (salinity 0.1–3‰), between freshwater (<0.1‰) and seawater (3.5%). Slightly brackish water (1,000–3,000 mg/L) can sometimes be used for irrigation; moderately-heavily brackish water (3,000–10,000 mg/L) requires desalination. Rich in sodium, chlorine and other ions, it tastes bitter and causes gastrointestinal discomfort if drunk directly.
2. Core Challenges
High salinity causes soil salinization, chloride ions corrode equipment, and TDS exceeds WHO’s 500mg/L drinking standard, harming long-term health. These issues limit utilization in areas like Ningxia.
III. Technological Breakthrough: Brackish Water Desalination Methods
Desalination is key to brackish water utilization, with a system dominated by Reverse Osmosis (BWRO), supported by complementary technologies.
1. Mainstream Technology: Reverse Osmosis (BWRO)
BWRO accounts for over 90% of the global market, costing 60% of seawater desalination. It uses high pressure to force water through a semi-permeable membrane, retaining salts (desalination rate 97–99%), with energy consumption 3.2–4.5 kWh/m³ and 70–78% recovery. Used in Algeria’s 12 brackish water plants (242,000 m³/day), China’s rural water projects, and Middle East desert emergency supply.
2. Auxiliary Technologies
Electrodialysis (ED/EDR) and EDI suit low-salinity brackish water (1,000–5,000 mg/L), with low energy and maintenance costs, used in Shandong’s Wudi project and Texas rural communities. Nanofiltration (NF) (1,000–3,000 mg/L) removes hardness while retaining minerals, used in European water quality improvement. Thermal desalination (MED/MSF) handles high-salinity water (>8,000 mg/L) with 75% thermal efficiency, used in Middle East oilfields. Capacitive Deionization (CDI) (TDS <2,000 mg/L) is low-energy for small-scale use; new membranes boost BWRO efficiency by 45% and extend life by 50%.
3. Technological Upgrading
Low-carbon and resource utilization drive upgrades: photovoltaic-wind-RO systems replace 60%+ fossil energy; Zero Liquid Discharge (ZLD) extracts lithium/potassium from brine; Xinjiang’s "freshwater + hydrogen + fertilizer" project has a <4-year payback.
IV. Global Practices
Algeria invested 2 billion euros in 12 BWRO plants (242,000 m³/day), planning 35 more to boost capacity 18x. The UAE and Saudi use skid-mounted BWRO for desert supply. China’s Xinjiang developed low-cost agricultural desalination; Shandong’s Wudi plant (100,000 tons/day) costs 2.9 yuan/m³. The U.S. Texas uses BWRO for strategic water; Mexico’s northern border relies on ED desalination.
V. Practical Dilemmas
Costs (3–6 yuan/m³) limit agricultural use (70% of global water). Inland brine disposal is costly and polluting. Only 10% of brackish water is used, with many seeing it as "useless", worsened by poor infrastructure in developing regions.
VI. Future Outlook
The global brackish water market grows 18% annually, with China’s 2025 scale exceeding 12 billion yuan. AI, IoT and new energy will build "zero-carbon desalination". By 2030, brackish water will supply 200 million people, becoming a key arid-region water source.
Conclusion: Brackish water, long ignored, is a critical solution to global water scarcity. Desalination advances turn it into usable water, driving a global "blue revolution". Unlocking this resource is a strategic choice for sustainable development, with brackish water set to become a core pillar of global water security in the next decade.
