- Crustaceans of the type called copepods (Copepoda) are appearing in NYC tap water. Several species are present.
- The primary species is Diacyclops thomasi, a very common type of copepod. It begins life measuring about 90 microns (.09 mm) and grows up to about 0.8 mm (males) and 1.4 mm (females) in about five weeks time. [1 inch = 25.4 mm]. [1 mm = 1000 microns].
- A second species, Mesocyclops edax, is also present. Studies have shown that D. thomasi and M. edax alternate in a cyclical fashion in dominating the copepods population of a habitat. Samples taken in June contained D. thomasi exclusively, while July’s samples included a significant representation of M. Edax. [Both D. thomasi and M. edax are both of the same Order – Cyclopoida.]
- Another species, Skistodiaptomus pygmaeus, is appearing in smaller quantities. They are slightly larger, measuring up to 1.2 mm (males), and are wider in diameter as well. [S. pygmaeus is of another Order of copepods – Calanoida.]
- Other species are likely present, but in small quantities.
The Source of the Infestation:
- The organisms that are found at the tap come from the reservoirs. [Research has shown that there is no basis to the initial suspicion that these creatures originate in the water mains.] Reservoirs are essentially man-made lakes, and contain a regular ecosystem, including algae, copepods (and other micro-organisms, such as water fleas (Cladocera), rotifers, nematodes, ostracodes, amphipods, etc.) and fish. These are not infestations, but rather essential components of a healthy ecosystem. Copepods feed on algae, which would otherwise multiply and deplete the water of dissolved oxygen. They in turn are food for the fish. Planktonic copepods are present in reservoirs, lakes, and other bodies of slowly moving water throughout the world.
- The reason they are turning up at the tap is that NYC is exempt from the federal and state requirements of municipal water supply filtration. Drinking water is drawn from the reservoirs at ~60 feet below surface level into large tunnels (~16 ft. Æ ) , and aside from the addition of chlorine and fluoride, arrives at the tap the way it left the reservoir. Therefore, organisms that are typically found in the open waters of a lake (species that are planktonic or limnetic, such as the three mentioned above) are present.
- Copepods of the Cyclops variety do not lay eggs into the open water. Rather, the eggs hatch inside special sacs attached to the female, which concurrently disintegrate. These eggs are very delicate, and will not survive in the water distribution system. Although Calanoid species do lay “resting” eggs that are extremely durable (these eggs help the species survive draught or freezing conditions), the overwhelming majority of copepods in the reservoirs and distribution system are Cyclops. Therefore, there is little reason to be concerned that copepod eggs may bypass a home filtering system and create infestation downstream of the filter. [Egg size is typically 50-70 microns].
- Copepods are present the whole year, although their population varies somewhat over the seasons. Detailed information and photographs of copepods that are likely to be found in fresh water lakes and reservoirs in our area can be found at the following website: http://www.glsc.usgs.gov/greatlakescopepods/
- In 1994 and 1995 the DEP undertook detailed studies of the copepod (and other zooplankton) population of the reservoirs. These studies document the presence of copepods (and other zooplankton) in all the reservoirs. These studies are on file at the OU, and are available upon request.
- Water fleas (Cladocera) are also planktonic, but many species are present in large numbers for only several weeks a year. They are also much more delicate than copepods, and are less likely to survive the trip to the tap. They have appeared at the tap in large numbers only sporadically.
- Nematodes, amphipods, and ostracodes all live at the bottom of reservoirs and lakes, rather than in open waters. They are thus less likely to be sucked into the effluent of the reservoirs. Isolated discoveries of all these organisms have been found in NYC tap water, but in frequencies low enough to be halachically unimportant.
- Rotifers are common, but they are extremely small (~0.1mm) and are generally considered microscopic. They cannot be recognized with the unaided eye.