In a small saucepan bring the water to a boil. Remove from heat and add in gelatin, stirring to dissolve completely. Let cool to room temperature, about 15 minutes.

Once cooled, stir in the lime juice, tequila and Cointreau. Set aside.

To prepare lime cups, cut the limes in half lengthwise and using a spoon, scoop out the flesh. Pour the jello mixture into the limes and transfer to the refrigerator to set, about 4 hours or overnight.

To serve, slice limes into wedges and top with coarse salt.