Next you put the lingonberries, the water, and the sugar in a large saucepan and boil for about 15 minutes. While the lingonberries are boiling set the oven for about 100°celcius and heat up some glass jars for about 10 to 15 minutes (you'll need these to put the jam in later).
When your jam is done remove the saucepan from the stove and also remove any "foam" that might have appeared.
Immediately put the lingonberry jam into the clean and hot glass jars that you've heated up in the oven and put a lid on them. Fill the glass jars to the top. It is really important that you do all this straight after you've removed the saucepan from the stove, and while both the jam and the glass jars are still hot. The whole idea is to allow as little air as possible in the jar and thereby preserving the preserve better. When the jam cools off inside the jar it sucks the lid to a tighter grip which further increases the effect of preservation.
Finally store the jars with your delicious lingonberry jam in a cool place.