Re-boiled water is flat — it has lost its dissolved oxygen.

A splash of hot water, swirled and tipped out. Keeps the brew hotter.

…and one for the pot, if you are feeling traditional.

Black tea: boiling. Green tea: ~80°C, or it turns bitter.

Guessing leads to stewed, bitter tea. Use a timer.

Last lets you judge the strength. First is gentler on the leaves. Choose your side and defend it.