Combine water, rice flour, and sugar in a saucepan over medium heat. Cook, stirring constantly, until the mixture thickens, about 5 minutes.
Mix milk, rose water. saffron, and cardamom together in a bowl; add to rice mixture. Bring to a boil and stir until there are no clumps, about 5 minutes.
Carefully ladle hot mixture into 6 cups; garnish each with 3 pistachios. Refrigerate for at least 1 hour.
