Batch treatment of water (0.2 to 240 L) using Fe0 (44,000–77,000 nm) in a diffusion environment operated (at −8 to 25 °C) using: (a) no external energy; (b) pressurized (<0.1 MPa) air; (c) pressurized (<0.1 MPa) acidic gas (CO2); (d) pressurized (<0.1 MPa) anoxic gas (N2); (e) pressurized (<0.1 MPa) anoxic, acidic, reducing gas (H2 + CO + CO2 + CH4 + N2), reduces the salinity of water. Desalination costs increase with increasing NaCl removal. The cost of reducing water salinity from: (i) 2.65 to 1.55 g·L−1 (over 1–24 h) is $0.002–$0.026 m−3; (ii) 38.6 to 0.55 g·L−1 (over 210 days) is $67.6–$187.2 m−3. Desalination is accompanied by the removal, from the water, of one or more of: nitrate, chloride, fluoride, sulphate, phosphate, As, B, Ba, Ca, Cd, Co, Cu, Fe, Mg, Mn, Na, Ni, P, S, Si, Sr, Zn. The rate of desalination is enhanced by increasing temperatures and increasing HCO3−/CO32− concentrations. The rate of desalination decreases with increasing SO42− removal under acidic, or pH neutral, operating conditions.