The older one gets, the less effectively one's body maintains thermoregulation. Those with limited incomes may not have electricity or AC, or may try to limit expenses by using it sparingly. People who do a lot of work outdoors aren't necessarily at greater risk if they use a little common sense. Of course, when perspiration is dripping off of us, we aren't cooling off very well. As we perspire, we lose both fluids and electrolytes, especially sodium.
Fluid loss leads to increased core temp., leading to more fluid loss, etc.
This means that if you rely on thirst as a signal to drink, you're roughly half way to significant dehydration. Drink before, during, and after periods of exertion. Protect yourself from the sun - wear hats, long sleeves, sunscreen, etc. The recent findings on sunscreen merely reinforce the concept that sunscreen alone isn't great idea. Offer cool towels or damp cloths around the neck, armpits, and groin.