Obesity and impaired glucose homeostasis in older adults place these individuals at risk for diabetes. Dehydration, glucose homeostasis, and insulin resistance are related; while aging and dehydration are associated with decreased glucose tolerance, weight loss can improve glycemia. For older adults following hypocaloric diets, additional water consumption may lead to greater weight loss. Further more, research sug- gests an association between insulin resistance and the body water retention hormone, arginine vasopressin (AVP). Analysis of the association between plasma copeptin (an AVP derivative) and fasting glucose, insulin, and homeostasis model assessment of insulin resistance (HOMA- IR) may provide further insight into the rela- tionship between dehydration and diabetes risk. Our objective was to investigate the possibility that increased water consumption among older adults (n = 29, BMI = 31 ± 1 kg/m², age = 62 ± 1 years) could improve glucose homeostasis be- yond that observed with weight loss, as well as associations between plasma copeptin and dia- betes risk. This retrospective analysis utilized data from a previous investigation, in which obese/overweight older adults were assigned to one of two groups: 1) Water: consume 500 ml of water prior to three daily meals over a 12-week hypocaloric diet intervention, or 2) Non-water: hypocaloric diet alone. In the present analysis, fasting plasma glucose and insulin, HOMA-IR, and plasma copeptin were evaluated, and com- pared to urinary specific gravity (USG), drinking water consumption, and body weight. Analyses performed using group assignment, volume of drinking water consumed or among a subgroup pair-matched for weight loss and sex did not reveal significant differences between groups. However in the full sample, plasma insulin concentration was associated with USG (r = 0.512, P < 0.01) and copeptin (r = 0.389, P < 0.05), and HOMA-IR was associated with USG (r = 0.530, P < 0.01) at week 12. Improvements in fasting insulin for water group participants (−8.5 +/− 4 pmol/L) were also detected. Associations be- tween hydration and insulin resistance support the need for future investigations addressing hydration status and diabetes risk.