September 24, 2003
A: FROM MENTOR JOAN LUSK IN RI
I think you are thinking clearly about the situation: if the pumps
stop for lack of electricity, there might be a failure to pump in
chlorine or bacteria might have time to multiply more; and an
overdose of chlorine to cure that problem might then be a problem
itself. But, like you, I'm only guessing. I found several sites you
might look at to follow up:

http://www.excelwater.com/eng/b2c/about.php this one lets you select
various kinds of problems with the water supply - too many suspended
solids, or metals, or bacteria - and various ways to solve the
problems. Bear in mind that it's a commericial site (.com) and will
recommend the products it sells... but the explanations looks
reasonable.

http://www.maritimetreasures.com/w/Water_Purification/Principles_of_Wa
ter_Quality_Control_0750636580.htm this is a popular textbook, for
civil engineers. There might be a copy in a library near you. I
wouldn't expect it to be light recreational reading... but it ought
to be thorough.

http://www.h2o2.com/h2o2update/volume1/smdfmc.html and this one
addresses the use of hydrogen peroxide instead of chlorine to kill
bacteria. A problem with chlorine is that large amounts of it need
to be stored near water treatment plants, and it is a very poisonous
gas if it escapes and is inhaled. When it is stored near population
centers, the prospect of terrorism leading to release of chlorine gas
is very serious, and some cities have switched to using hydrogen
peroxide, which is much less toxic. I have to credit either
Frontline or 60 Minutes for alerting me to this situation.