Toxic waste waters polluted with high levels of chemical byproducts of various industrial processes (e.g., waste water held in industrial holding ponds) are treated using gas hydrate to extract and remove fresh water from the polluted water, thus reducing the volume of toxic waste water inventories. Extracting fresh water by forming and removing the hydrate raises the concentration of dissolved materials in the residual concentrated brines to levels at which the residual fluid is suitable for use as an industrial feedstock. Furthermore, so raising the concentration of the residual brine will cause certain mineral species to precipitate out of solution, which mineral species are separated from the fluid and may be put to other uses, as appropriate. Food products are also advantageously concentrated by means of gas hydrates.