Rooh Afza: Substitute with Jam-e-Shireen or Naurus.
Milk: Use full fat, low fat or any milk of your choice. To make vegan, use coconut milk or almond milk.
Watermelon: Use deseeded watermelon that's been chopped into small cubes. Instead of chopping a whole watermelon, I got pre-sliced watermelon from the grocery store and chopped it into small cubes myself.
Freeze the watermelon cubes: to make it more chilled and delicious.
Storage: This drink is best enjoyed immediately. But to make ahead you can mix the milk and rooh afza beforehand, and store in the fridge. Prior to serving, add the ice cubes and watermelon cubes, stir and serve. The drink can be stored in the fridge for up to 1 day.