What is the ideal temperature of water when adding to pie dough ingredients?

The ideal temperature of water when adding to pie dough ingredients is ice cold. Using ice cold water helps to keep the fats like butter or shortening in the dough solid, which is critical for achieving a flaky texture in the final pie crust. This cold temperature prevents the fat from melting into the flour too quickly during mixing, allowing for the development of a proper flaky pastry structure once baked.

Lukewarm water, while it might help with mixing the dough more easily, can lead to the fats starting to melt, which can compromise the flakiness of the crust. The other temperatures, boiling and room temperature, would similarly cause the fats to melt too much before baking, resulting in a denser, less desirable texture for the pie crust. Therefore, keeping the water cold is essential for achieving the perfect pastry.