The best thing to drink when working in the heat to stay hydrated is water which is the best hydrating drink that keeps your body healthy and hydrated.
You can also drink some Gatorade or other Sports drinks that can help keep your body hydrated during the summer heat.
When working in the hot summer heat you should also take plenty of breaks to cool off when possible and then also drink water or other liquids before you feel thirsty.
Never wait until you're actually thirsty before drinking water or other hydrating liquids because when you wait you can become dehydrated.
So always drink water throughout the day and drink around a gallon or more of water throughout the workday to prevent dehydration.