Is it permissible to perform ablution with rainwater collected in a place frequented by dogs, while pure water is available?

There is no harm in performing ablution (Wudu') and ritual bathing (Ghusl (definition)) with water collected from rain, even if dogs have licked it, as long as it has not been altered by impurity. This is based on the Prophet's (peace and blessings be upon him) saying: "Indeed, water is pure; nothing makes it impure." This applies to water that reaches two qullatayn or more. As for less than that, there is a difference of opinion among scholars.