Start by rinsing the raspberries gently under cold water to remove any dirt or debris. Drain them well and set aside.
In a large pot, combine the rinsed raspberries and water. Stir to mix the ingredients.
Bring the mixture to a boil over medium heat. Once boiling, reduce the heat and let it simmer for about 15-20 minutes. You want the raspberries to break down and release their juices.
Using a fine mesh strainer, carefully pour the raspberry mixture through the strainer into another pot or bowl. Press down on the raspberries with a spoon to extract as much juice as possible. Discard the seeds and pulp.
Return the strained raspberry juice to the pot over medium heat. Add the sugar and stir until it is fully dissolved. Allow the mixture to come to a gentle boil again.
Reduce the heat and simmer the syrup for another 10-15 minutes, or until it thickens slightly. Keep in mind that the syrup will thicken more as it cools.
Remove the pot from heat and let the syrup cool to room temperature. Once cooled, transfer the syrup into clean glass jars and seal tightly. Store in the refrigerator.