TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Process: In the process, solubility of water in the dry ionic liquid (in mg/kg) is at least 10 times higher than the dry medium's solubility in the same dry ionic liquid (in mg/kg). The process comprises: drying the hydrated ionic liquid and reusing the dried ionic liquid as dry ionic liquid in the dehydration process; continuously removing the hydrated ionic liquid and continuously replenishing the hydrated ionic liquid with dry ionic liquid; and contacting a dehydrated medium comprising a gas, a liquid or a supercritical fluid with a water-containing material to extract water from the water-containing material into the medium, to produce a dehydrated material and a water-containing medium, and contacting the water-containing medium with a dry ionic liquid choline salt to dehydrate the water-containing medium. The process further comprises: separating the dehydrated medium from the hydrated ionic liquid and recirculating the dehydrated medium; drying the hydrated ionic liquid to produce a dry ionic liquid; and recirculating the dry ionic liquid. The step of drying of the hydrated ionic liquid comprises heating the ionic liquid to temperature in excess of 80 degrees C. The water-containing medium is a pressurized gas having a pressure of at least 3 MPa, a liquefied gas or a supercritical fluid. In the process, stream of the water containing medium is contacted with a stream of the dry ionic liquid in a counter current fashion. The water content of the water-containing material is reduced by at least a factor 3. Preferred Components: The dry ionic liquid is a salt of choline and a carboxylic acid. The water-containing medium, when it is contacted with the dry ionic liquid, contains 0.01-10% of water, percentage being calculated by weight of dry medium. The water-containing medium comprises at least 50 wt.% of dry medium of carbon dioxide (preferred), nitrous oxide, methane, ethane, ethylene propane, cyclopropane, propylene and/or butane. The water-containing material comprises intact pieces of animal or plant tissue.