What episode does Piper meet Leo?

She meets him officially in 1x03 "Thank You For Not Morphing" but she first saw him in season 3 episode name Pre-Witched. While walking down the street with Prue. She is talking to Prue about how she thinks she will never meet the right guy when Leo bumps into her, she turns and smiles then apologizes. They continue walking when she turns again and smiles at him. You then see him orb away which hints that he knew they were witches before they knew.