It's not hot enough. Black tea is usually brewed with boiling hot water around 95 - 100 °C. Green tea is usually brewed a bit lower than that at around 80 °C.

It's not hot enough. Black tea is usually brewed with boiling hot water around 95 - 100 °C. Green tea is usually brewed a bit lower than that at around 80 °C. But the domestic hot water supply is typically around 50 °C, to prevent burns. It'll be very weak, and probably taste a bit off. Same with coffee, or anything else that requires boiling hot water.