Add tea bags, sugar and boiling water to a 1 litre mason jar. Steep for 3-5 minutes.
Remove tea bags and add lemon juice. Mix well. Cover and refrigerate the lemon tea concentrate until ready to use.
To serve, add chilled sparkling water to the lemon tea concentrate. Mix well.
Place a handful of ice cubes in 4 tall drinking glasses. Pour over the sparkling lemon tea and garnish with lemon slices.
(Alternatively, pour lemon tea concentrate in 4 tall drinking glasses filled with ice cubes. Top up with sparkling water and garnish with lemon slices)