DPH: Invertebrates in Public Water Supplies

Invertebrates in Public Water Supplies


This fact sheet provides general information pertinent to the recent finding of two organisms in a drinking water supply in Connecticut.   While these organisms are not themselves a health risk, a “boil your drinking water” advisory was released as a prudent precaution.  This fact sheet explains why this advisory was needed and answers questions related to the detection of these organisms in drinking water. 




Surface water supplies in Connecticut undergo a variety of treatment processes to ensure a healthy supply free of particles, organisms and pathogens.  These treatment processes include filtration to remove any material floating in the water and chlorination to disinfect the water.  However, temporary disruptions in water treatment systems may affect water quality and lead to prudent avoidance recommendations such as boiling the water or switching to bottled water until the problem is fixed.  These measures are rarely needed; testing is ongoing to make sure that problems do not develop. 


There is a recent report of two organisms being found in a Connecticut water supply.  These are tiny invertebrates called copepods and rotifers.  They are less than 1 mm in length but can still be seen with the naked eye.   These organisms are quite common in Connecticut’s surface waters but are normally kept out of drinking water supplies by filtration systems.


Are Copepods and Rotifers a Health Concern?


These organisms are not a human health concern even if ingested in drinking water.  They will not attach to the lining of the stomach or intestines, nor will they multiply or form colonies in your stomach.   Both of these organisms can be carriers of other microscopic organisms (protozoa), but none of the protozoa are known to be a health concern to people.  Therefore, on their own, copepods and rotifers do not appear to be a threat to public health.    


However, the presence of these organisms in a public water supply’s finish water indicates some problem with the system.  It may be a signal of improper filtration; a breach in supply or distribution lines, or some problem with the way the water is stored and treated.  Therefore, when these organisms are found in the finish water, the water treatment plant must investigate how they are getting into the system and correct the problem. 


Should I Drink the Water if these Organisms are Present?


Since these organisms are not known to harm public health, it's possible that the water can be consumed without a health risk.  However, since the presence of copepods and rotifers is abnormal and indicative of a problem in the treatment system, it is prudent to boil the water before drinking it.  This is just in case other organisms that are normally filtered out of the raw water, such as cryptosporidium and giardia, have made it past the filters and are also present in the finish water.  These organisms are infectious and can harm human health.  Because they are rarely in public supplies, they are not routinely tested for.  Fortunately, boiling destroys cryptosporidium, giardia and any other microorganisms that might be of concern.  This provides a precautionary line of defense against the possibility that such organisms have made their way into the finish water along with the detected copepods and rotifers. 


Would I need to Use Boiled Water for Showering and other Water Uses?


No.  Routine water uses such as bathing, showering, hand washing brushing of teeth, and the washing of clothing and dishes is fine without boiling the water.  Any potential health concern is only from ingested water. 


Are there Any Special Concerns for Babies, the Elderly or Immuno-Compromised?


No.  If the only evidence of a water treatment issue is copepods and rotifers, boiling of water for drinking is sufficiently prudent and protective for everyone. 


If This Occurs, How Long Would I have to Continue Boiling My Water?


This situation can take some time to fully investigate, test and back-flush the water treatment system.  Only when this is done and it can be verified that the filtration system is back to normal with no pathogens in the water, then the “boil your water” advisory can be rescinded.  This will hopefully be no more than a few days. 


Where Can I Get More Information?


CT DPH’s Drinking Water Section: 860-509-7333


The Metropolitan District Commission (MDC):   860-278-7850

Content Last Modified on 2/17/2011 8:14:44 AM