Background Dehydration is a health risk for miners in tropical regions of Australia. However, it is not known whether dehydration poses a health risk to miners working in temperate regions of Australia. Methods A cross-sectional study of 88 miners from two underground mines was undertaken in south-eastern New South Wales, Australia. Participants had their height, weight, waist circumference and hydration status measured and completed a self-administered questionnaire on fluid intake, access to water, and socio-demographic characteristics. Health and Safety managers were surveyed about guidelines relating to healthy work and lifestyle behaviours which impact/influence hydration. Results Hydration tests indicated that more than half of the miners (approximately 58%) were dehydrated (Urinary Specific Gravity (USG) >1.020) both before and after their shift, with three workers pre-shift and four workers post-shift displaying clinical dehydration (USG>1.030). Overall, 54.0% of participants were overweight and 36.8% were obese. Miners who commenced the shift with poor hydration status were 2.6 times more likely to end the shift with poor hydration, compared to those who commenced the shift with good hydration (OR 2.6, 95% CI 1.06, 6.44). Miners who had a mean USG result for the entire shift indicating dehydration were more likely to be obese (42.9%) and have a waist measurement in the high risk range for metabolic complications (40.8%) than those workers that were adequately hydrated for their entire shift (29.4% and 14.7% respectively). Some guidelines promoting healthy lifestyles and supportive work environments were in place, but there were limited guidelines on healthy weight and hydration. Conclusions Dehydration, being overweight and obesity were linked issues in this cohort of miners. Strategies are needed to: adapt the workplace environment to increase water accessibility; encourage appropriate consumption of water both at work and at home; and to promote physical activity and good nutrition to maintain healthy weight.