Color-enhanced scanning electron micrograph showing Spirochaetes bacteria from a cover slip on the wall of a plastic drinking cup. The cup was used for urban tap water and was only rinsed with that water and the walls were left wet until the next use a few hours later. Within a month, the cover slip became slightly foggy. Whatever accumulated on it was fixed in glutaraldehyde and examined by SEM. In addition to a small number of cocci and bacilli, Spirochaetes figured prominently. Image width: 6.4 micrometers. Magnification: 15,625x if the image is printed 10 cm wide.