Add 200ml room temperature water into a small saucepan.
Turn on the heat and bring the water to a boil.
Turn off the heat and add in the butterfly pea flowers.
Cover the pot with a lid and let the butterfly pea flowers steep in the hot water for 3 minutes.
Take off the lid and strain the water. Press the flowers with the back of a spoon to remove as much butterfly pea flower extract as possible. Discard the flowers.
Pour the strained tea back into the saucepan.
Add sugar and turn on the heat to low.
Stir occasionally until the sugar is all dissolved.
Bring the butterfly pea syrup to a boil and turn of the heat.
Pour the syrup into a pitcher or jug.
Top it with the remaining 1300ml cold or chilled water.
Next, add the lemon juice. The butterfly pea flower juice will turn purple as soon as you add lemon juice to it.
Stir the lemonade. Keep it refrigerated until ready to be served.
To serve the butterfly pea lemonade, add ice cubes into a drinking glass and pour the lemonade. Garnish with the lemon slices.