Combine peanut butter, granulated sugar, and water in a medium saucepan over medium-high heat. Stir continuously with a whisk or wooden spoon as mixture heats to dissolve the sugar and fully mix the peanut butter into the liquid.
Once the mixture reaches a boil, the mixture should be fully blended. Reduce heat to low and let simmer for about 10 minutes, stirring occasionally, until mixture has thickened.
Pour syrup into a mason jar or bowl and place in fridge to cool completely before using.
When ready to use, shake well. You may want thin syrup out a bit by heating it in the microwave for 20-30 seconds.