I would think it would have to be really hard water to leave visible spots. However, after washing model I usually do a final wipe with rubbing (isopropyl) alcohol. Now, the more concentrated mixes of that stuff can take off acrylics, but it is fine for lacquers and enamels. For acrylics, you'd want to use the weakest stuff your drugstore carries, and let that acrylic set up well for a couple of days- I'd even test a sample of your paint dried for awhile before using alcohol on it. Even with enamels and lacquers I do not douse the model with alcohol, merely dampen a fine cloth and do a quick once over. I find this takes any dust, residue, or fingerprint oil off that plain water doesn't.