There are small, portable stills you can take with you. I used to use one to make distilled water for washing my contact lenses, when I used them because I am allergic to mercuric compounds like thimerosal.

In some countries, you can go to a pharmacy and get distilled water used for administering intravenous medications. In others you can Google or look in local Yellow Pages or the equivalent - in Australia, there are sources of distilled water. Chemists (drugstores), doctors and others would be able to direct you to sources.