Combine water and sugar in a saucepan over high heat, stirring to dissolve the sugar. Once the syrup looks clear, add the jalapeno slices, discarding the stem ends. Bring to a boil, and cook hard for 12-15 minutes to infuse the simple syrup with the oils from the jalapeno.
Remove from heat, and transfer the syrup to a heat-safe measuring cup or bowl. When cooled to room temperature, pour through a fine mesh sieve to remove the jalapeno slices and seeds and store in an airtight container in the fridge. Reserve the lightly candied jalapeno slices for drink garnishes and to use as a delicious addition to salsas or salads.
The heat of jalapenos can vary, and this syrup is meant to just have a hint of spice. For stronger jalapeno flavor and a thicker syrup, increase the reduction time of the syrup. Be careful not to add too much time though, as this might result in caramelization of the syrup.