Emergencies: Water purifier

Could our clean water supply ever be challenged?

Just in case, I recently purchased a portable MSR Guardian Water Purifier!
This model provides the following benefits.
Physically removes in one easy step:

VIRUSES
Like:
Norovirus / Norwalk
Rotavirus
Hepatitis A virus

BACTERIA
Like:
E. coli
Shigella
Salmonella
Cholera

PROTOZOA
Like:
Giardia
Cryptosporidium
Amoebae

PARTICULATE
Like:
Sediment
Silt
Dirt