Many of the instructions in this section and others on this site call for clean water. Tap and bottled waters often contain minerals that may be deposited on your items. Distilled or deionized water are always preferred, then filtered water. Otherwise, use the cleanest water available. If you can get only a very limited quantity of distilled or deionized water, save it for your final rinse, and rinse thoroughly. Remember that your water is picking up contaminants as you use it, so change the water frequently.
Water is distilled by boiling and then condensing the steam. This leaves behind impurities such as minerals that might be deposited on objects. The process also sterilizes the water, but it does not guarantee that the water is free of bacteria, unless the container has also been sterilized. Distilled water is usually available in supermarkets, drugstores, and hardware stores.
This is water that has had charged particles or ions removed. This removes the minerals that are often present in water that are most likely to cause problems with sensitive objects by leaving a film or residue on the surface. Deionized water may still contain bacteria or other substances, so it is not necessarily safe to drink. The most likely source for deionized water is a person or company that has a deionizer. Companies who detail cars or clean windows commercially are possible sources.
While less desirable than either distilled or deionized water, filtering may remove many undesirable substances from tap water such as iron, that could potentially damage sensitive devices. In addition, municipal water sources are often compromised after a disaster, and may contain a higher-than-normal amount of contaminants. Water filters may be in scarce supply after a disaster, but if available, a “point-of-use” filter is relatively inexpensive ($25 or so), and easy to attach to a faucet.
Tap water often contains minerals such as calcium or iron that may be left behind when cleaning. These can damage sensitive items such as circuit boards, storage media, or art objects. However, tap water may be the cleanest water available.
Bottled water is often sold as much or more for flavor as for purity, and so is likely to contain as many or even more minerals as your municipal water supply. It is possible that it is cleaner, but do not assume that it is.