In a pot, bring water to a boil. Add tapioca pearls and cook, stirring occasionally on medium heat for half an hour. Remove pot from heat and let sit for 5 minutes. Transfer tapioca pearls to a strainer, rinse under cold running water and then drain well. Set aside.

In a saucepan, whisk together coconut milk, milk and sugar. Bring to a boil and then remove from heat. Set aside to cool.

In a mixing bowl, combine cooled coconut milk mixture, tapioca pearls and diced mangoes. Cover with plastic wrap and then chill in the fridge for at least an hour.