Heat the water, lemon, ginger, and salt in a saucepan over medium heat. Bring to a simmer for 5 to 15 minutes, depending on how strong you want the flavors to be. Remove from the heat and check the temperature; it should be roughly 190°F.

Strain through a mesh strainer to remove the lemons and ginger from the water. Check the temperature to see if it has reduced to about 175°F. If not, transfer to another cup until it reduces to the temperature.

Place the sencha in a teapot and pour the flavored water in. Allow the tea to steep for 3 minutes. Pour into glasses and enjoy immediately.