Re: How safe is tap water when a boil water order ends?

	When dealing with the government, nothing is ever as simple as we think it
could or should be.  The drinking water system is no exception.  Congress
has placed the responsibility for defining drinking water safety with the
Environmental Protection Agency (EPA), which delegates enforcement to the
states and ultimately places the burdens of operation and monitoring on the
water utilities themselves.  Unlike food processors, who can recall food
that they find to be defective or hazardous, water utilities have only the
Public Notification system at their disposal.  The EPA Public Notification
Handbook (EPA 816-R-00-010 — June 2000) is available at:
.
	Public notifications may result from detection of a hazard in the public
water supply or from failure to test for hazards according to EPA
regulations.  That is, EPA requires sampling and testing of drinking water
at intervals, based on the size of the population served.  If a utility
fails to do this, they are required to issue a Public Notification. 
Ordinarily this will only include a recommendation to boil water if there
is microbiological evidence of a hazard.  There are three “tiers” to the
notification system:
Tier 1 notice for violations or situations with significant potential to
cause serious effects due to short-term exposure;
Tier 2 notice for all other violations or situations with potential to
cause serious effects; and
Tier 3 notice for all other violations and situations not included in Tier
1 and Tier 2.
	Tier 1 notifications are supposed to reach everyone that is at risk within
24 hours (usually via the mass media), whereas 30 days are allowed for Tier
2 and a year for Tier 3, with mailings, postings, etc., as options. 
Obviously, if a Tier 1 notification has been put forth, the public should
be told the nature of the emergency and how they should respond.  A “boil
order” is one option.
	The question posed is about a “boil order” that started and ended while a
family was away from home.  Let’s assume they determine that the Public
Notification entailed a real threat, whereby they would have boiled the
water that they were going to drink if they had been at home.  Each
household has a single service connection to the passing water main,
typically out under the street in front of the house.  If no water was
being used in the home during the family’s absence, then whatever
contaminated water there was should have flowed on by and left the area. 
If water was used, or if this is a multiple dwelling unit from which only
one family was absent, there may be some risk.  
	At that point, a purposeful flush may be a reasonable idea.  Again,
however, one would want to think where the contaminated water might have
gone in the home while no one was there.  For example, if a faucet was
dripping, day after day, contaminated water may have been drawn all the way
to that faucet from the service connection.  On the other hand, if water
was used only via a programmed irrigation system, contaminated water may
not have entered the house itself.  Flushing the pipes would be necessary
only in the part of the home system that might harbor microbiologically
contaminated water.  If a toilet was found to have been leaking, the
reasonable thing to do would be to flush that toilet several times, in the
expectation that any contaminated water along the line would go directly to
the sewer.  Flushing toilets is probably a better way to “rotate” water
than running it in sinks or showers anyway.  If the toilet is not of the
modern, water-conserving type, each flush will consume 3 to 5 gallons of
water, so not many flushes should be needed to get rid of whatever water
was in the line.  There is no point in boiling water that no one is going
to drink, and any contaminated water that may have entered the house need
not go to the sink lines (for dishwashing or tooth-brushing, for example).  
	In fact, only a very small proportion (say, 1%) of “drinking water” is
actually ingested, and some people never drink tap water.  Still, Congress
has charged EPA with the responsibility to see that we can safely drink
water from public supplies anywhere in the country.  I don’t work for EPA,
but I have worked with them in some of their efforts, as well as with the
World Health Organization.  I also drink tapwater anywhere I go in the US,
but not necessarily in other parts of the world.  

Dean O. Cliver