Summarized List: Environments
When traveling through an area with a hot and dry climate, you should make sure to pack extra drinking water and protection from the sun's harmful rays. Extreme Heat is an environmental condition that can cause exhaustion, poor concentration, and even death.
Each successive level of Extreme Heat includes all effects of the levels below it.
Level 1: You take a -1 penalty to all physical ability and skill checks, and your exhaustion increases by 1 level every hour.
Level 2: You take a further -2 penalty to all checks, and the frequency of exhaustion increases to 1 level every 30 minutes.
Level 3: You take burning damage equal to your hit point increment minus your Constitution modifier every minute, or every round of combat. This damage ignores all armor. It's best to avoid Level 3 Extreme Heat whenever possible.
Drinking a glass of water (8 ounces) reduces your exhaustion level by 1 if the exhaustion is caused by heat. You can benefit from this effect only once per hour, so drinking water alone is only enough to stave off exhaustion in Level 1 of extreme heat.
Wearing clothing with the Cool property, or gaining the Heat Resistant status effect. Each level of either effect reduces the level of extreme heat effects you experience by 1.