Sprinkle the unflavored gelatin evenly over the cold filtered water in a wide bowl. Let it bloom undisturbed for 5 to 10 minutes.
Bring 3 cups of filtered water to a rolling boil. (Optional: steep with hibiscus or mint for 5 minutes, then strain).
Pour the boiling water directly over the bloomed gelatin. Whisk continuously until completely dissolved and clear. Whisk in the sweetener until dissolved.
Allow to cool slightly, then stir in the fresh lemon juice and vanilla extract.
Pour the mixture into ramekins or molds. Refrigerate for at least 4 hours, or overnight, until completely firm.