The river rises just to the east of the Wiltshire village of Redlynch, near Salisbury. It then flows east across the county boundary into Hampshire. Here it flows north of the village of Wellow and Wigley before joining the Test between Totton and Redbridge.
Another similarly named waterway in Hampshire is Black Water. Black Water is a small stream which flows eastwards across the New Forest, passing under Rhinefield Ornamental Drive, before joining Ober Water and Highland Water just north of Brockenhurst to form the Lymington River.