If a fly falls into clean water in a small container and dies, with no separate impurity present, the Hanafi rule for creatures without flowing blood applies.
The water is not spoiled on account of that death alone. The ruling arises from the kind of creature, not from the large quantity of water.
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Impurity in Stagnant and Running Water, Large Ponds, and Aquatic Creatures
If a fly falls into clean water in a small container and dies, with no separate impurity present, the Hanafi rule for creatures without flowing blood applies.
The water is not spoiled on account of that death alone. The ruling arises from the kind of creature, not from the large quantity of water.