Medical instruments and procedures. Distilled water has a high purity that makes it ideal for sterilizing medical instruments, leaving no sediment or residue. Surgeons use it to sterilize and prevent infection and cross-contamination, and emergency personnel use it to clean wounds. Dentists use distilled water to rinse their mouths and remove bacteria. It is also preferred for continuous positive airway pressure (CPAP) machines, as it prevents bacterial growth. Hemodialysis machines use ultrapure water to filter waste from the blood. Laboratory tests. Nothing in distilled water interacts with or affects the accuracy of laboratory tests.