What kind of water is inside the medical pressure reducing valve?

Specially treated distilled or deionized water. These waters are highly purified to remove impurities and ions from them to ensure that they do not pose any hazard to patients when used in medical equipment. Medical pressure reducing valves usually consist of a switch that can be rotated to allow the user to select the desired gas type and flow setting, and a digital display that shows the current gas flow and pressure.