Heat exhaustion occurs when blood volume displacement to the skin causes marked cardiovascular stress. In the on-duty police officer, heat exhaustion can lead to headache, dizziness, nausea, diminished fine motor function, and confusion. If not treated, this can progress to heatstroke, which is a life-threatening medical emergency. In hot weather, an officer should be well hydrated before beginning his/her shift. Generally, replacing body fluid losses through drinking water can prevent dehydration. Medications and medical conditions can contribute to dehydration or increased heat production. The goal of hydration is to provide the body with water, sodium, potassium, chloride, and bicarbonate in order to maintain a state of normal homeostasis. When a person's body becomes dehydrated, it is less able to dissipate the heat that it naturally produces. This can lead to rapid elevation in body temperature and heat exhaustion. Medical studies have demonstrated that even a 1-percent decrement in hydration can result in decreased physical and mental performance. This article includes descriptions of various hydration gear for officers to have with them while on duty.