Peel the ginger and grate finely. It must be at least 2 tablespoons. Mix with the juice from the lemon.
Using a funnel, pour the sugar and yeast into a 1 liter plastic bottle. Do not use a glass bottle as it will not withstand the pressure of fermentation. Let the ginger run into the bottle with the juice. Fill the bottle halfway with still water.
Shake the neck of the bottle and fill the bottle up to approx. 5 cm below the rim. Let rise in a warm place for 24 hours. Put the bottle in the refrigerator for 24 hours to stop fermentation.
Pour the contents of the bottle through a sieve and serve.