How does a public water supply (PWS) work?

A water supply has several stages:

• Water source
• This is usually a reservoir or lake
• Some supplies draw groundwater from wells
• Contamination might be introduced here, but the next stage would probably take it out
• Water treatment
• Water from a lake is usually filtered and chlorinated.
• Chemicals are removed and germs are inactivated
• Water storage
• Large tanks or reservoirs may be an inviting target
• Water distribution
• This system could be damaged or contaminated

You can take a virtual tour of the treatment plant in Greensboro, NC, at http://www.greensboro-nc.gov/water/Supply/treatment.htm

Water is a national security issue