Every hiker knows to carry a water bottle. But when hiking in the heat, exactly how big should that bottle be? To decide, consider the following:

In the heat, you lose about .5 to 1 quart of water and electrolytes per hour through sweating. Drink enough to replace this amount.

For a day-long hike, you may find it impossible to carry all the water you'll need. When planning your hike, research the trail's designated safe drinking water resources. As a backup plan, pack water purification tablets that you can add to water from streams.