If the ambient temperature is only $70^\circ\text{F}$ or $80^\circ\text{F}$, what potential issue exists during sun tea brewing?

The water may never get hot enough to properly steep or sterilize itself

When the ambient air temperature is relatively low, such as only $70^\circ\text{F}$ or $80^\circ\text{F}$, a major food safety risk emerges for sun tea. In these cooler conditions, the water contained within the jar often fails to absorb enough heat to reach temperatures required for effective steeping or, more importantly, high enough to sterilize the contents. Consequently, the liquid can remain suspended within the bacterial temperature danger zone for the entire duration of the brewing process, promoting bacterial growth rather than inhibiting it, thus making the tea potentially unsafe.