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Athletes and researchers could benefit from a simple and universally accepted technique to determine whether humans are well-hydrated, euhydrated, or hypohydrated. Two laboratory studies (A, B) and one field study (C) were conducted to determine if urine color ( ${\text{U}}^{\text{col}}$ ) indicates hydration status accurately and to clarify the interchangeability of ${\text{U}}_{\mathrm{col}}$ , urine osmolality ( ${\text{U}}^{\text{osm}}$ ), and urine specific gravity ( ${\text{U}}^{\text{sg}}$ ) in research. ${\text{U}}_{\mathrm{col}}$ , ${\text{U}}_{\mathrm{osm}}$ , and ${\text{U}}_{\mathrm{sg}}$ were not significantly correlated with plasma osmolality, plasma sodium, or hemato-crit. This suggested that these hematologic measurements are not as sensitive to mild hypohydration (between days) as the selected urinary indices are. When the data from A, B, and C were combined, ${\text{U}}_{\mathrm{col}}$ was strongly correlated with ${\text{U}}_{\mathrm{hg}}$ and U„_sm. It was concluded that (a) ${\text{U}}_{\mathrm{col}}$ may be used in athletic/industrial settings or field studies, where close estimates of ${\text{U}}_{\mathrm{sg}}$ or ${\text{U}}_{\mathrm{osm}}$ are acceptable, but should not be utilized in laboratories where greater precision and accuracy are required, and (b) ${\text{U}}_{\mathrm{osm}}$ and ${\text{U}}_{\mathrm{sg}}$ may be used interchangeably to determine hydration status.

A common practice in sports science is to assess hydration status using the concentration of a single spot urine collection taken at any time of day for comparison against concentration (specific gravity, osmolality, color) thresholds established from first morning voids. There is strong evidence that this practice can be confounded by fluid intake, diet, and exercise, among other factors, leading to false positive/negative assessments. Thus, the purpose of this paper is to provide a simple explanation as to why this practice leads to erroneous conclusions and should be curtailed in favor of consensus hydration assessment recommendations.