The importance of developing a valid assessment measure of human hydration status for clinical and field use is recognized by the military community as a high priority medical technology gap (MOM ICD v1.3, 2008). In far forward locations (levels I-II), orthostatic testing or gross symptoms are most commonly used to estimate hydration status (Manning et al., 2007). However, level I-II methods share symptoms with numerous other maladies and are insensitive until dehydration is severe or becomes debilitating (Levitt et al., 1992; McGee, 1999). Definitive hydration assessment in rear roles of medical care (levels III-V) requires invasive serial blood and/or urine measurements (Feig, 1977; Mange, 1997). Thus, a field-expedient technology that provides an accurate, non-invasive assessment of hydration status would improve medical triage by allowing better fluid-electrolyte management by medics in theatre (point of care), and by medical personnel in the rear levels of care (treatment and return to duty).