Short terms effects of dehydration include reduced physical capacity and reduced mental alertness in the short term. Persistent dehydration is associated with kidney stones and bladder cancer.
"This pilot study investigated the extent of dehydration in six logging crews by measuring the specific gravity of urine. Thirty one loggers provided a urine sample and gave information on their fluid intake for that day. The specific gravity of the urine samples was measured and the weather conditions monitored. Twelve loggers (30%) were found to be inadequately hydrated."
Report from the Centre for Human Factors and Ergonomics, Volume 2, No. 2, 2001.