Begin by placing the raspberries and sugar into a medium saucepan. Use a fork or potato masher to crush the raspberries, allowing their juices to flow. Heat the mixture over medium heat until it begins to simmer, stirring occasionally. Once bubbling, remove from heat and let it cool for about 10 minutes.
Using a fine-mesh sieve, strain the raspberry mixture into a large pitcher, pressing down firmly to extract as much juice as you can. Discard the leftover solids.
Pour the freshly squeezed lemon juice into the pitcher with the raspberry juice and mix well.
Gradually add the carbonated water to the pitcher, stirring gently to combine without losing the fizz.
Fill glasses with ice cubes and pour the raspberry citrus fizz over them. If desired, top with lemon wedges and extra raspberries for a beautiful presentation.