Engineering components tend to come off the line with particulates or stains as a result of contact between coolant and material scraps during fabrication. Considering this lacks quality in finish and is in some cases unsafe for moving parts, components are regularly cleaned of impurities before leaving the factory doors.
To leave the component spot free, deionised water is preferably used. This type of wash will give the desired finish without the damage or corrosion that you may experience with a chemical cleaning solution. Deionised water also has the added benefit of being more cost effective and more energy efficient than using distilled water.