For years, we've been told that desalination is too energy-intensive and expensive for widespread use. Yet Elon Musk has repeatedly claimed the costs are "insanely low." Which perspective is closer to reality? This analysis examines the true energy requirements and costs of seawater desalination, revealing its potential to address global water scarcity.

This examination concentrates specifically on desalination's energy consumption and economic viability, setting aside important but separate environmental concerns like brine disposal. This focused approach allows for clearer understanding of desalination's core cost structure.

To better grasp desalination's economic impact, we'll explore extreme hypothetical situations—such as supplying all U.S. household water through desalination or providing drinking water for the entire global population. While unrealistic, these scenarios help quantify desalination's cost scale.

Modern desalination primarily utilizes two methods:

• Thermal Desalination: Heats seawater to evaporate and separate water from salts, then condenses the vapor into fresh water while discharging concentrated brine.
• Reverse Osmosis: Forces seawater through semi-permeable membranes under pressure, filtering out salts and impurities to produce fresh water.

While both methods work, thermal desalination consumes 3-5 times more energy than reverse osmosis. Consequently, most modern plants use reverse osmosis technology, which forms the basis of our analysis.

Reverse osmosis technology has achieved remarkable efficiency improvements. In the 1970s, desalinating one cubic meter of water required about 20 kWh of electricity. Today, that figure has dropped to 2.5-3.5 kWh. The theoretical minimum energy requirement stands at 1 kWh/m³, suggesting potential for further advancement.

For our calculations, we'll use 3.5 kWh/m³ as a conservative baseline—some plants already operate below this threshold.

If all U.S. homes received their water through desalination, how would this affect electricity demand?

With average household water use at 1,135 liters daily, complete desalination would increase residential electricity demand by approximately 13%. In the UK, where households use less water (349 liters/day) but face higher electricity prices, the increase would be about 15%.

Examining U.S. household electricity consumption reveals that desalination's annual requirement (1,450 kWh) compares to major appliances like dehumidifiers, remaining significantly below water heaters, heating systems, or air conditioning usage.

While 1,450 kWh annually might be manageable for wealthy nations, this exceeds the total electricity consumption of many developing-world households. Even meeting the WHO's minimum water standard (50 liters/person/day) through desalination would require 64 kWh annually—equivalent to Malawi's per capita electricity consumption.

This disparity highlights global energy poverty more than desalination's inherent energy demands.

Considering humans need only about 3 liters daily for drinking (allowing for some waste), supplying all 8 billion people would require 31 TWh annually—just 0.1% of global electricity production. Even if one-third of humanity faced drinking water shortages, the annual requirement would be approximately 10 TWh.

Meeting WHO's full basic water standard (50 liters/person/day) globally would require 511 TWh annually—about 1.7% of worldwide electricity generation.

Beyond energy expenses, large-scale desalination demands substantial capital investment—often the greatest barrier for many nations, similar to renewable energy projects where upfront costs outweigh long-term affordability.

Current global desalination costs typically range from $1-2.5 per cubic meter, though exceptional cases like Israel's Sorek B plant achieve $0.41/m³, with one study of 107 plants identifying $0.27/m³ as the lowest cost.

At U.S. industrial electricity rates (~$0.09/kWh), the energy cost alone for desalination would be $0.45/m³ (3.5 kWh × $0.13/kWh). In high-cost areas like California, this could reach $0.90/m³. Since energy typically constitutes one-third of total costs, complete costs might reach $1.50-$2.00/m³ in expensive markets.

Translating to personal expenses:

• U.S. average (310 liters/day): $154 annually
• UK average: $159 annually
• WHO minimum standard: $38 annually
• Basic drinking water needs: Just $2.30 annually—less than bottled water costs in many countries

For crisis situations, these costs are indeed remarkably low. However, $38 annually remains burdensome for those living on $2/day—representing over two weeks' income.

Agriculture presents desalination's greatest challenge, consuming 70% of global freshwater (exceeding 90% in some tropical nations). Replacing even partial agricultural water would increase many countries' electricity demand by 50-100%, making current technology impractical for widespread farming use.

Producing 1 kg of wheat with desalinated water would cost $0.66 in water alone—triple wheat's market price. For corn, water costs would equal the crop's value. Only high-value crops or water-efficient systems (like indoor agriculture) might justify desalination for agriculture currently.