Giardia is the microbial parasite that causes giardiasis, a diarrheal disease. There are several species of Giardia, including Giardia intestinalis, Giardia lamblia, and Giardia duodenalis, which are present in the feces of infected humans and animals.
The parasite can enter water sources through a number of routes including sewage overflows, improperly working sewage systems, and runoff from agricultural and urban areas. Surface water and shallow wells are particularly vulnerable to contamination by Giardia.
If you suspect your water is contaminated, contact a state certified laboratory about getting your water tested.
Giardia may be killed or inactivated by bringing the water to a rolling boil for one minute (longer in higher elevation). It should then be allowed to cool in a clean, sanitized container with an air-tight cover and refrigerated.
Some point-of-use filters will remove Giardia, but not all. According to the CDC, home water filters with the label “reverse osmosis”, “absolute pore size of 1 micron or smaller”, “tested and certified by NSF Standard 53 for cyst removal,” and “Tested and certified by NSF Standard 53 for cyst reduction” will remove or reduce the Giardia contamination.