What is the difference between purified water and distilled water?

i need to know im suppose to use distilled water in my cpap machine and i bought purified.

Purified water and distilled water are essentially the same thing: water which has had all impurities and minerals removed. The two have gotten to that point, however, by two different methods.

Purified water has been processed by reverse osmosis or deionization to produce water which has no dissolved solids. Distilled water has been boiled and the steam has been collected, leaving the solids (and impurities) behind. Distilled water is more commonly used in medical uses (like your cpap machine).

My dad uses a cpap machine and he uses distilled water. But in all honesty, purified water is indistinguishable from distilled water beyond the method of purification.

They are the same. It is only the method to create them that is different.

Purified uses reverse osmosis to filter out everything.
Distilled is boiled and then condensed.

purified may mean that water has been made pure by adding chemicals, distilled water is water that has been boiled and the end result is the evaporation process where the steam is cooled and the resulting water is called distilled, so it usually does not have any chemicals in , if you boil water and the pot goes dry, and there is a dry residue in the bottom of the pot that is what will collect in your machine, and in effect ruin the machine

Purified water is nothing more than water run through some sort of filtration unit. Distilled water is pure H2O with any contaminants removed.