Place the pomegranate juice in a heavy bottomed sauce pan and heat over medium-high heat until you see steam whipping up from the pot and the beginning stages of a simmer. Remove from the heat and stir in the sugar until it has completely dissolved.
Stir in the orange blossom water and set aside until the grenadine has cooled completely. Once cooled store in an airtight container in the refrigerator for up to a month.
