In a large saucepan, bring the water, lemon juice, sugar and thyme to a boil. Cook until a candy thermometer reads 120 °C (250 °F).
Add the blueberries and stir gently. Bring to a boil and remove from heat. Pour the jam onto a large baking sheet and let rest for 1 hour at room temperature. Pour the jam back into the saucepan and bring to a boil. Remove from the heat and remove the thyme.
Pour the jam into sterilized jars. Cool and refrigerate.