Cranky? Cant focus? Have a drink of water! A recent small study suggests that even very mild dehydration may affect our mood and even our ability to concentrate. 25 "Average" women were "dehydrated" with diuretics and moderate exercise. Mood, concentration and mental acuity testing was done before and after the dehydration took place. Overall, mental ability wasnt affected but increased perception of task difficulty and lower concentration was noted. Small study with room for more investigation. When in doubt, take a drink (of water that is!)