Keep your head covered. Only sip water when you really need it. The water here is going to be purified, if these people have been here for any length of time, but don't drink a ton of it because you're just going to sweat it out again.

If you stop sweating entirely, or get dizzy, nauseous, or have a throbbing headache or weak pulse, get inside immediately and drink water because those are signs of heatstroke.