This weekend we have had guests – and they asked me what tap water looked like under the microscope. We filled 18 Eppendorf 1.5ml centrifuge tubes with tap water and centrifuged them at 10000 revs/minute for 10 mins. We then pipetted off the top 95% of the water and moved the remaining water into a single tube and centrifuged it again at similar settings. Removing the top 90% of that tube and then putting the bottom few drops onto a slide and using x40 objective revealed that there is was a small amount of grit and organic debris only. We could not see bacteria. This suggests that our tap water is pretty clean and safe.