Waterborne parasites pose a health threat. Understanding how to test for their presence in water sources helps identify contamination and allows for necessary precautions. This guide covers common parasites, testing methods, result interpretation, and post-testing steps.
Common Waterborne Parasites
Two of the most frequently encountered waterborne parasites that cause illness in humans are Giardia lamblia and Cryptosporidium parvum. These microscopic organisms are typically found in water sources contaminated by human or animal waste. When ingested, they can lead to gastrointestinal diseases known as giardiasis and cryptosporidiosis, respectively.
Giardia lamblia causes giardiasis, an infection of the small intestine characterized by symptoms such as diarrhea, abdominal cramps, bloating, nausea, and fatigue. Symptoms can appear anywhere from 1 to 3 weeks after exposure and may last for several weeks or even months if untreated. Cryptosporidium parvum leads to cryptosporidiosis, often called “Crypto,” which also presents with watery diarrhea, stomach cramps, vomiting, and loss of appetite. While healthy individuals usually recover within a few weeks, the illness can be severe and life-threatening for those with weakened immune systems. Both parasites are resistant to chlorine disinfection, highlighting the need for specific testing and treatment methods.
Methods for Testing Water
Testing water for parasites primarily involves professional laboratory analysis, as at-home kits are generally not reliable for definitive identification. The process typically begins by contacting a state-certified or EPA-accredited laboratory specializing in water analysis. These laboratories provide specific instructions and sample collection kits, which are important for obtaining a valid sample. Proper sample collection involves using sterile techniques, ensuring adequate sample volume, and prompt delivery to the lab, often requiring refrigeration. For instance, a minimum sample size of 100 gallons is sometimes recommended for parasite testing.
Laboratories utilize various methods for analysis, including microscopic examination to directly observe parasite oocysts or cysts. Additionally, molecular methods like Polymerase Chain Reaction (PCR) are increasingly used due to their high sensitivity and specificity in detecting parasite DNA. At-home screening kits are generally not reliable for confirming parasite presence, lacking the sensitivity and specificity of laboratory tests.
Interpreting Test Results
Understanding a water test report requires familiarity with common terminology and what a positive or negative result signifies.
A common phrase you might encounter is “not detected” (ND) or “below detection limit” (BDL), which indicates that the specific parasite was not found in the sample at measurable levels. Conversely, a report indicating “presence of oocysts/cysts” means that Cryptosporidium oocysts or Giardia cysts were identified in the water sample. The report may also provide a concentration, though for parasites, the mere presence is usually concerning due to their low infectious dose. It is advisable to consult with the testing laboratory, a public health official, or a water quality expert to fully understand the implications of your results and determine the appropriate next steps.
Steps After Testing
The actions taken after receiving water test results depend entirely on whether parasites were detected.
If parasites like Giardia or Cryptosporidium are detected, immediate action is necessary to prevent illness. Boiling water for at least one minute is an effective method to kill both Giardia and Cryptosporidium. Alternatively, using bottled water or a water filter certified to remove cysts (e.g., those meeting NSF/ANSI Standard 53 or 58 with an “absolute 1 micron” pore size, or reverse osmosis filters) can provide safe drinking water. It is also important to contact local health authorities or your water utility company for guidance on remediation, especially for private well owners. They can offer advice on well disinfection, identifying the source of contamination, and implementing long-term solutions.
If the test results indicate no parasites were detected, this is reassuring, but it does not eliminate the need for ongoing vigilance. For private well owners, annual testing for bacteria, nitrates, total dissolved solids, and pH is recommended, as these can be indicators of potential contamination pathways for parasites. Maintaining good water management practices, such as ensuring proper well construction and sealing, protecting the wellhead from surface runoff, and avoiding the disposal of waste near the well, remains important for preventing future contamination. After events like floods, retesting is particularly important due to increased risk of contamination.