The source case places impurity at one side and permits use of the opposite side. If impurity enters near the centre, that argument cannot automatically be applied identically to every point.
The reach and effect of impurity must be assessed in relation to the particular place where water is taken, considering the extent and movement of the water.
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Impurity in Stagnant and Running Water, Large Ponds, and Aquatic Creatures
The source case places impurity at one side and permits use of the opposite side. If impurity enters near the centre, that argument cannot automatically be applied identically to every point.
The reach and effect of impurity must be assessed in relation to the particular place where water is taken, considering the extent and movement of the water.