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.

Read the full report on dehydration here. (PDF)