Bring milk to a gentle simmer over medium heat, about 5-7 minutes.
Add water, flour and sugar and mix with a whisk to integrate the sugar and flour into the milk.
Reduce heat to low and stir continuously with a wooden spatula for 30 minutes.
Add the rosewater and continue to stir for 15-25 additional minutes or until the pudding has visibly thickened. Taste the pudding to make sure the flour has softened and no longer feels gritty.
Remove from the heat and using a ladle divide the pudding into individual serving bowls.
Place the pudding in the refrigerator and serve chilled.