This question has been investigated through many research projects and clinical trials. At Stayhealthy we reviewed a number of published works on the subject and even conducted our own clinical trial. We have developed the Stayhealthy Hydration Index (SHI), which calculates on an individual basis, your specific hydration status based on broad population averages and studies. On the graph showing your hydration results is a line marked with zero. This represents the threshold for acceptable hydration, and should be considered the minimum level of hydration your body needs. A measurement above zero is desirable. Each person's zero point is calculated by determining the hydration of their lean mass (everything except fat), plus the water contained in their body fat. Just as physical makeup varies from person to person, so does the zero point.