Answer: -A water filter will remove solids, not the dissolved minerals (hard water) that can interact with some chemicals and leave deposits on film and paper. The easiest way to get distilled (or de-ionized) water is to buy it by the gallon at a drug store. I would not trust water from a de-humidifier because it tends to grow crud that can cause problems. -At one time, and this was quite a while ago, the use of distilled OR deionized water was not recommended as it was thought to affect the surface tension of the film/developer - Chapman discussed it in the predecessor mag to Phototechniques. It was a problem with the charge on the gel in the emulsions - but as I said this was many years ago. An interesting science experiment for one of the kids - take a water filters (say from an Ametek W-10 whole house filter) and weigh it "dry". Put the filter on for a month, completely dry and then reweigh the filter. This should give you a good idea of the crud which goes through our municipal filtering systems. Here in suburban NJ our plumber tells of the stuff which gets through the filter systems (sometimes there is an "oops" at NJ American Water"). One more thought on water - filter the hot side - the calcination on the hot water heater can get into the system and result in particulate drying on your film.