What serious condition might arise in someone who works outside in a physically demanding job in August, sweats a lot, and consumes only large volumes of water throughout the day (for 6 to 8 hours)

Hyponatremia

Explanation:

In medicine, hyponatremia refers to a medical condition where there's a low level of sodium in the blood.

One of the main causes for hyponatremia is having prolonged periods of exercise (and therefore sweating a lot) combined with drinking large volumes of water without electrolytes. Because of the sweating and the large volumes of water, the kidneys start malfunctioning and they can't regulate the amounts of sodium properly.

In this example, a person works outside in a physically demanding job in August, sweats a lot and consumes large volumes of water throughout the day, we can see that this person meets the criteria mentioned in the previous paragraph to develop signs of hyponatremia.