Place a small plate in the freezer. Sterilize two jam jars by placing the jars and their lids (screw top) in a big pan of water and bringing the water up to the boil. Make sure the jars don't contain any air bubbles. Boil the jars for 10 minutes while you proceed with the recipe. After ten minutes, turn off the heat and leave the jars and their lids in the hot water until use.
Wash the berries and pick any remaining stems from them. In a medium-sized pan, combine the berries with the sugar and the water. Stir together with a wooden spoon. Gently heat the berries over low heat, stirring until the sugar has dissolved. Once the sugar has dissolved, crank up the heat and bring the berries to a boil. Leave to gently simmer, uncovered, for 10 minutes, stirring occasionally. After 10 minutes, the berries should have softened and can easily be squashed against the side of the pan with a wooden spoon.
Take the plate out off the freezer and take the jam off the heat. Spoon a little of the jam onto the chilled plate and place it back in the freezer to set for 1 minute. Take the plate out of the freezer again and push your finger through the jam to check if it has reached setting point. If the surface of the jam wrinkles when you push your finger through, it's ready. If it doesn't, boil the jam for another 1-2 minutes and repeat the setting test.
Take the jars out of the hot water with thongs or a pair of forks and place them upside down on a clean tea towel. Ladle the jam into the warm, sterilized jars, leaving a 1-cm (¼ -inch) headspace. Wipe the rim of the jars clean with a clean, damp cloth, seal the lids and leave the jars to cool upside down. If you don't have enough jam to fill one of the jars all the way up, store the jar in the fridge and use it over the next couple of weeks.
NOTE: the jars need to be hot to prevent them from breaking when filled with the hot jam.
Store in a dry, dark place and use within a year.
Recipe by The Tough Cookie at https://thetoughcookie.com/2013/08/26/wild-blueberry-jam/