Is it sufficient to pick up dry mouse droppings to remove the impurity, or must water be used?

Some scholars, like Sheikh al-Islam Ibn Taymiyyah, held the view that rat droppings are excused due to the difficulty of guarding against them. Ibn Taymiyyah chose to excuse small amounts of all impurities, and Ibn Ziyad from the Shafi'i school issued a fatwa excusing them if their prevalence becomes widespread. Removing these droppings is sufficient; there is no need to wash what they have fallen on.