Bring 1 cup of water to a full rolling boil. The water should have large bubbles before using it.
Pour the boiling water into a medium mixing bowl and whisk in the gelatin for about 1 minute until completely dissolved. The mixture should look smooth and glossy.
Let the mixture cool for about 2 minutes so it is still warm but no longer steaming heavily.
Stir in the tequila, cold water, and optional triple sec and lime juice until fully combined. The mixture should remain smooth without separating.
Carefully pour the mixture into plastic shot cups, filling each about three-quarters full. A measuring cup with a spout helps prevent spills.
Place the cups on a tray and refrigerate for 2–4 hours, or until fully set. The tops should feel firm and spring back lightly when touched.
Garnish with a small lime wedge and a light sprinkle of salt if making a margarita-style version.
Serve chilled directly from the refrigerator for the best texture and flavor.