Brewed tea should be refrigerated as it can grow bacteria. In fact, tea can grow klebsiella, enterobacter or E. coli, all of which can be harmful to humans.
Tea leaves, like all food, have natural bacteria on them, even in their dried form. Home cooks should brew tea at 195 degrees Fahrenheit for three to five minutes to kill bacteria. Nonetheless, bacteria can still grow in tea, so once it has reached room temperature, place it in the refrigerator for storage.
Tea aficionados can also brew tea in the refrigerator. Just put tea bags or loose-leaf tea in a jug or pitcher and add water, in the same ratios that would normally be used for tea.