If there were no restrictions on hunting deer in the United States, hunters would have a plethora of hunting options available to them. Bows and crossbows are accurate and quiet, but rifles can fire at a longer distance with more accuracy.
However, what if a hunter was committed to hunting in the healthiest, fairest way possible? Would they trade in their rifle and bow for a throwing spear and hunting knife?
It’s possible they might be willing to put in the added work to enjoy the greater reward of not sacrificing their ideology and health.
A similar dichotomy is appearing in the extraction industry, as more people are steering away from conventional solvent extractions due to potential health concerns. In the cannabis industry, for example, solventless and non-toxic solvent extractions are gaining in popularity.
Just as a hunter may want a healthier, greener way to hunt, consumers are taking their health and ideology into shops and dispensaries.
Critical water (H2O) extractions may one day become a go-to, popular method. This technique comes in two varieties. Subcritical water extraction keeps water in a liquid state under pressure at a temperature less than 374°C. Above that temperature, the process becomes known as a supercritical water extraction. The goal is to decrease the relative permittivity of H2O until it takes on solvent properties.  [Graphic 2: Mass Transfer – Advances in Sustainable Energy and Environment Oriented Numerical Modeling]
People are already experimenting with this cleaner approach. In 2008, a paper looked at how subcritical water extractions compared to more conventional methods in Lavandula stoechas (topped lavender). 
Researchers noted that subcritical water extraction yielded 124 components while hydrodistillation (HD) and organic solvent extraction under ultrasonic irradiation (USE) yielded 94 and 65, respectively. They found that the subcritical water extraction produced more oxygenated compounds (e.g. linalool) but fewer monoterpenes (e.g., α-pinene). At 60 atmospheres (atm), temperatures of 100°C and 125°C produced high yields with slightly different compounds, but 150°C decreased the quality and yield of the extract significantly. 
Critical water extraction methods may be less toxic and provide a more desirable product.
Interestingly, the EPA investigated the use of subcritical water for “polar and non-polar organic pollutants from contaminated solids.” The organization has used this extraction method to “remediate soils which were highly contaminated with PAHs and pesticides.”
Botanical extractors are always on the hunt for improved methods, even if they seem simpler. Some are willing to give up a rifle for a throwing spear, especially when it means an extra element of eco-friendliness has been added. While critical water extractions might not overtake sub- or supercritical carbon dioxide in the cannabis industry, the prospect of the method is still interesting for replacing less environmentally friendly methods with one devoid of hazardous solvent waste.
- Asl, A.H., and Iran M. Khajenoori. “Subcritical Water Extraction.” Mass Transfer – Advances in Sustainable Energy and Environment Oriented Numerical Modeling, edited by Hironori Nakajima, 2012, doi: 10.5772/54993.
- Giray, E., et al. “Comparing the Effect of Sub-Critical Water Extraction with Conventional Extraction Methods on the Chemical Composition of Lavandula stoechas.” Talanta, vol. 74, no. 4, 2008, pp. 930-5. [Times cited = 67; Journal Impact Factor = 4.916]