In a saucepan, cover the lemons with cold water. Bring to a boil, then simmer for 30 minutes or until the lemons are tender, stirring several times during cooking. Drain and rinse under cold running water. Let cool for a few minutes.
On a work surface, cut the lemons in half. Remove and discard the seeds, then finely chop the lemon peel and flesh. Return to the saucepan. Add the sugar and water.
Cook over medium heat until a candy thermometer reads 223°F (106°C), about 20 minutes. Transfer to airtight containers or jars.
To sterilize the jars filled with marmalade, completely cover with water and boil for 10 minutes. Sterilized jars will keep for 1 year at room temperature, unsterilized for 1 month in the refrigerator.
Recipes with the "Healthy Pick" stamp have been evaluated by a registered dietitian member of the Ordre professionnel des diététistes du Québec.