The objective of this study is to establish reference values for non-invasive hydration status markers. Although there are no hypotheses associated with this study, the outcome will help advance the development of non-invasive hydration status monitors (described above and in H08-12; A-15208) capable of detecting dehydration from a single, static measure. The outcome that this research effort supports what is recognized by the military community as a high priority medical technology gap (MOM ICD v1.3, 2008).