Complex sentence: Stainless steel does not readily corrode, rust or stain with water as ordinary steel does; but, despite the name, it is not fully stain-proof, most notably under low-oxygen, high-salinity, or poor-circulation environments.
Split into simpler sentences: Stainless steel does not readily corrode, rust or stain with water as ordinary steel does. However, it is not fully stain-proof in low-oxygen, high-salinity, or poor air-circulation environments.