When I was in the hospital, my CPAP machine ran out of water. I asked for some tap water, and the nurse offered me some sterile water instead. At the time, I couldn't smell or taste anything, so it wasn't a problem.
It was after I got back home and tried on my mask. The stench had infiltrated every part of the mask, tubing and reservoir. It took a few rinsing, but I finally got the stench out.
Sterilized means that all the bacteria and viruses have been removed or killed, such as by UV irradiation or boiling.
Distilled means the water has been boiled, the steam collected, and condensed back into pure water.
