Miami's summer air holds about 22 grams of water per kilogram at 32°C and 80% relative humidity. That's a floating aquifer nobody drinks. Instead of shipping it away as sweat and AC condensate, what if a single kilometer-tall tower pulled it down as liquid — using nothing but a hygroscopic liquid film and gravity?

The design borrows from industrial absorption chillers. A concentrated lithium chloride brine (roughly 40% LiCl by mass) has a vapor pressure well below humid ambient air. Trickle that brine down the inside of a vertical tower while humid air flows upward, and water vapor spontaneously migrates into the film. Diluted brine collects at the bottom; a solar-driven regenerator boils the water back out and recycles the salt.

The tower

• Height: 1,000 m (Burj Khalifa +170 m)
• Cross-section: 200 m × 200 m of packed structured aluminum sheets — think a cooling-tower fill scaled to skyscraper dimensions
• Wetted surface area: ~4 × 10⁷ m² (packing gives ~500 m² per m³ of volume)
• Airflow: passive stack draft plus assist fans — target 2 m/s upward velocity

How much water?

Volumetric air throughput: 200 × 200 × 2 = 80,000 m³/s. Air density ≈ 1.15 kg/m³, so mass flow is 92,000 kg/s. If the falling film strips 6 g of water per kg of air (a realistic ~30% approach to equilibrium), we harvest:

92,000 kg/s × 0.006 = 552 kg water/s
     = 47.7 million liters/day
     = 12.6 million gallons/day

That's the daily potable-water demand of roughly 150,000 Miamians — from one building.

The energy trap

Absorption releases the latent heat of condensation: 2,450 kJ per kg. Our 552 kg/s liberates 1.35 GW of heat inside the tower. Without rejection, the brine heats up, its vapor pressure climbs, and absorption grinds to a halt within minutes. So we plumb the tower with seawater-cooled tubes shedding that 1.35 GW into Biscayne Bay — essentially a district-scale cooling loop running in reverse.

Regeneration is the bigger bill. Boiling water back out of dilute brine costs a similar 2,450 kJ/kg, but a double-effect solar thermal regenerator can hit ~50% recovery efficiency, so real input is ~4,900 kJ/kg. Daily energy: 4.77 × 10⁷ kg × 4,900 kJ = 2.34 × 10¹¹ kJ ≈ 65 GWh/day. A 3 km² concentrated solar field at 25% efficiency in south Florida sun (~6 kWh/m²/day peak) covers it.

Why it might actually work

Unlike condensation dehumidifiers, the tower never chills air below its dewpoint — no compressor, no refrigerant, no phase change of the working fluid at the absorption stage. LiCl brine is already deployed in industrial dryers; the chemistry is boring, which is what you want at gigawatt scale. The tower doubles as a heat sink for surrounding blocks by pre-cooling exhaust air 8-10°C on the way out.

The catch

Corrosion. LiCl chews through stainless steel; you need duplex alloys or fiber-reinforced polymer packing, and every gasket becomes a maintenance item. A single brine leak into the harvested water stream contaminates the reservoir. And in a hurricane, you have a 1 km chimney full of 40% salt solution — the mechanical engineers will not thank you.