Cut the limes into small pieces and reserve 4 slices for garnish. Strain the juice from the pineapple slices and combine with the reserved pineapple juice. Set aside 4 pineapple slices for garnish and roughly chop the remainder.
In a pitcher muddle the limes and stir in the sugar. Add the chopped pineapple, and muddle a bit more. Stir in the pineapple juice and 1 cup water. Add tequila, if desired.
Serve in ice filled glasses garnished with pineapple and lime slices.