Place water, lemon juice, stevia, citric acid and lavender flowers into the Thermomix bowl and bring to a boil 8 min/100°C/speed 1. Pour into another jug to cool completely.
Strain through a nut milk bag to remove the solids.
I use 1 litre jars from Kmart with a pop lid, so add 1 tbsp sugar to each jar you are making, add 4 tbsp of strained active ginger bug. Top up with the lavender liquid and seal and shake.
Leave these on the kitchen bench for up to 48 hours, burping a couple of times a day to make sure you don't get an explosion. It may take longer than 48 hours to develop depending on the activity of your ginger bug. You will know you have bubbles once the jar is popping open with a bit of a bang when you burp it.
Refrigerate and serve over ice with a garnish of a lavender flower.