Mw. Lechevallier et Wd. Norton, GIARDIA AND CRYPTOSPORIDIUM IN RAW AND FINISHED WATER, Journal - American Water Works Association, 87(9), 1995, pp. 54-68
The American Water System has conducted extensive monitoring of its op
erations since 1988. Analysis of 347 surface water samples collected b
etween 1988 and 1993 showed that the prevalence rate of Giardia and Cr
yptosporidium was 53.9 percent and 60.2 percent, respectively. But bec
ause the parasite assay does not indicate viability or virulence, thes
e results do not necessarily indicate that these water systems were at
risk from waterborne pathogens. To supplement coagulation and filtrat
ion, the average system will have to apply sufficient disinfection to
reduce viable Giardia levels by 3.1 log(10). An analysis of existing d
isinfection practices shows that most systems are already applying dis
infectant at a level sufficient to reduce Giardia levels, However, the
proposed Disinfectants/Disinfection By-products (D/DBP) Rule may hamp
er the ability of water utilities to apply sufficient disinfection und
er current operating conditions. Careful integration of the D/DBP and
the Enhanced Surface Water Treatment rule is encouraged.