What is required if pure water is mixed with water whose purity has been nullified?

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When pure water is mixed with water whose purification capability is nullified, one must perform a complete ablution (Wudu) from each container of water and then pray one single prayer using both ablutions. This ruling is established because the obligation permits fulfilling the obligatory act with certainty without hardship. This is analogous to a situation where both containers were pure but insufficient on their own.