Limitations and Cautions on Data Use
REMINDER: The ICR data were collected as part of a national research project to support development of national drinking water standards. They should NOT be used to determine local water systems compliance with drinking water standards, nor should they be used to make personal judgements about individual health risks.
The ICR data were collected from July 1997 to December 1998. All the data have been verified, and the database is complete. EPA will use the data to identify national and regional patterns, not to reach system-by-system or treatment plant-by-treatment plant conclusions. The data that you will see are from individual samples. What EPA will evaluate is the degree to which the samples represent overall water quality.
It is difficult to accurately estimate the numbers of protozoan cysts without testing large quantities of water, and this is not always feasible. The actual levels of these pathogens in source water may be much higher than those found by the tests.
However, the current ICR detection method does not distinguish between species of Giardia and Cryptosporidium that may cause illness and those that do not. The method may also misidentify algae as a Cryptosporidium.
With the ICR detection method, both false positive (microbe is counted when it is not actually present) and false negative (microbe is not counted when it is present) results are possible.
The ICR detection method cannot determine whether the microbes are alive or whether they are able to cause illness.
Better detection methods are currently being developed to detect and count protozoa.