Water

For the purposes of plant tissue culture, distilled or deionized water is most commonly used. Distilled water consists of water that has been turned to vapor through heating, and re-condensed. Deionized water has been run through special columns that remove cations and anions, as well as organic materials.

For research purposes, ultrapure water may also be used. Ultrapure water (sometimes referred to as 18.3 water, for 18.3 megaohms per centimeter electrical resistance) is considerably more expensive to produce, and is not worth the added expense for production purposes. It has some utility in research, such as that for nutrient deficiency experiments, or where particularly good water may be required for whatever purposes.

A rough gauge of the quality of water is its resistance to electrical flow, hence the "18.3" designation of ultrapure water. It should be noted that water of such high quality diminishes immediately upon exposure to air as it absorbs carbon dioxide, forming carbonic acid, which is a weak electrolyte. For comparison, depending upon the quality of the feed water and the techniques used for distillation, distilled water usually runs somewhere around 300-500 kiloohms of resistance once it has been exposed to air. Fresh distillate on a good machine can run 1-10 megaohms/cm.