Using water loss as a percentage of body weight, between what levels do heat cramps and heat exhaustion start?

Between 5-8% of body water loss

Explanation:

Mild dehydration, naturally occurs from 3%, at this point most people can manage and cope with it, and its relatively easy to recover from. From 5% decrease, fatigue and dizziness creeps in, which are good factors for heat cramps and heat exhaustion. Finally, any loss above 10% is regarded as sever, exceeding 15% can lead to death.

the answer is life structure