This video was hosted on Vidme, which is no longer in operation. However, you might find this video at one of these links:
Post Collapse: SHTF: WROL: Water supplies, things are not always what they seem
June 6 2017
This video provides an example of a possible post collapse water supply which is not as it seems. Water sources needed to be recon-ed to determine possible contaminants prior to desiding whether to use them and or how to treat the water. This pristine appearing lake actually suffers occasional contamination from a up stream sewage pump station during heavy rain events.