Lately, a new question has been popping up online: what's the difference between sterile water and distilled water?

Sterile water has usually been boiled to kill anything living in the water, but it still has other things in it. Distilled water is made to get you as close to pure H2O as possible - no bacteria, no chemicals, no impurities, etc.

There are some big differences, so we went to our resident water expert and asked him to break it down:

What is the difference between ‘sterile’ water and ‘distilled’ water?

 By Eldon C. Muehling

Sterility is a property of water while distilled water is the type of water produced by the distillation process of water treatment. When applied to water, the word sterile means that there are no viable (able to reproduce) bacteria, viruses or any other type of viable microorganism present.

When water is distilled, the first step is to boil the water. The process of boiling kills virtually every microorganism that may be present.

The next step in the distillation process is the formation of steam which is lighter than air. The steam thus rises, leaving any dead organisms behind, and thus producing sterile water, at least for the time being.

If there are any air-borne bacteria in contact with the distilled water some of them will enter the distilled water, but they are not of any great concern. (They can’t live in distilled water and are non-pathogenic but could show up in a standard plate count for bacteria.) Distilled water will also be free of virtually any chemicals.

Two other processes besides boiling that produce sterile water are chlorination and ozonation. While these processes produce sterile water, the dead bacteria remain in the treated water where they could provide nutrition for any living bacteria that appear. For this reason, excess chlorine or ozone would need to be in the water for the water to remain sterile. Chlorination produces a bad taste and also does not destroy or remove protozoa (single-celled animals). Chlorinated water could, in most cases, contain various chemicals (due to harmful chlorine by-products). Ozonated water does destroy protozoa, leaves no bad tastes, and produces virtually no harmful by-products.

In summary, distilled water is sterile, but sterile water isn't always distilled. Distillation takes it another step toward perfection.

Distilled water is still your best choice.