Wash off the lemon balm and thyme and dry them on a piece of kitchen roll. Quarter a piece of ginger about the length of a fingertip and place in a pot with the other ingredients. Chop or pluck the thyme and lemon balm and add to the pot.
Pour the hot water over the whole thing, let it cool and stir a few times. Let it steep in the fridge overnight. Depending on the taste, more or less lemon juice can be added.