One of us has done their math terribly wrong. A cubic meter is 1000 liters. If we assume (as you said) that 1m^2 can produce 50L per day, you would need 20m^2

One of us has done their math terribly wrong. A cubic meter is 1000 liters. If we assume (as you said) that 1m^2 can produce 50L per day, you would need 20m^2 (1000/50) to produce a cubic meter. Not 20,000m^2(!!). So for 600k cubic meters of desalinated water you'd need 12 million m^2 (or 12km^2 or ~3000 acres), which sounds very doable.