Ulangan 21:4

21:4 and bring the heifer down to a wadi with flowing water, ¹  to a valley that is neither plowed nor sown. ²  There at the wadi they are to break the heifer’s neck.

[21:4]  ¹ tn The combination “a wadi with flowing water” is necessary because a wadi (נַחַל, nakhal) was ordinarily a dry stream or riverbed. For this ritual, however, a perennial stream must be chosen so that there would be fresh, rushing water.

[21:4]  ² sn The unworked heifer, fresh stream, and uncultivated valley speak of ritual purity – of freedom from human contamination.