Put water, sugar, and pineapple in a medium-size saucepan and bring mixture to a boil.
Once boiling, lower heat and let simmer for about 15 minutes, until mixture has thickened a bit and pineapple is breaking down.
Strain mixture into a bowl, being sure to press down on the pineapple to extract as much juice as possible.
Keep syrup in bowl or pour into a mason jar and place in fridge to cool completely before using. Syrup will continue to thicken as it cools.