Top 5 Water Contaminants
depending on other conditions that could allow cultures of ammonia-oxidizing
bacteria (AOB) to thrive in the water storage and distribution system.
With the presence of AOB, also called nitrifying bacteria, any residual
ammonia in the system left over from formation of chloramines, could be
converted to nitrite. Accumulated sediment in cracks, crevices or on the
bottom of storage tanks are potential locations for AOB to thrive.
are the benefits to using chloramine instead of chlorine in the distribution
system? The benefits of chloramine compared with chlorine for distribution
system disinfections are:
- longer lasting disinfectant and ability to reach remote areas,
- effectiveness as a disinfectant for biofilms,
- tendency to form lower levels of regulated DBPs (e.g., THMs and HAAs), which are probable carcinogens (USEPA, 1998), and
- ability to minimize chlorinous or other objectionable taste and odors. Chloramine is more stable and lasts longer in the water in the distribution system because
it is less reactive than chlorine.
The water agencies that have converted
to chloramine report that customers note an improvement to the odor of
the water. Research on the taste-and-odor quality of drinking water has
demonstrated the benefits of monochloramine over chlorine. The San Francisco
Public Utilities Commissions (SFPUCs) change to chloramine helps ensure
compliance with more stringent federal and state drinking water quality
regulations. In San Francisco, chloramination has virtually eliminated
the presence of Legionella species in large building hot water heaters
(Flannery et al., 2006).
What are the drawbacks to using chloramine instead of chlorine in the
distribution system? The drawbacks of using chloramine compared with chlorine
for distribution system disinfection are:
- potential temporary deleterious
effects on older elastomeric materials sometimes used in some home appurtenances
and plumbing fixtures,
- vulnerability to the microbiological process
known as nitrification,
- potential formation of chloraminerelated DBPs
if precursor material is present in the source water (Kirmeyer et al.,
2004). The treatment precautions for hemodialysis clinics and fish cultures
must be taken both with chlorine and with chloramine (Amato, 2005). Certain
natural rubber products and their derivatives used in household appliances
(e.g., toilet tank valves, hot water heater dip tubes) will deteriorate
faster with chloramine than with chlorine (Reiber, 1993).
such effects are experienced, replacing these items with alternative materials
available in the plumbing and hardware stores will eliminate this temporary
nuisance rubber deterioration. Vulnerability of chloramine to nitrification
can be remedied by several practices, including:
- reducing the detention time of water in the drinking water storage reservoirs and low-use pipelines,
- keeping the system clean of deposits, which may harbor bacteria,
- flushing when necessary, and
- monitoring the system.
All these actions
have an additional benefit for customers by providing fresher, shorter
"shelf age" water. Typically, a change to chloramine has been preceded
and followed by distribution system capital improvements aimed at decreasing
water age such as: seasonal or permanent outages of water tanks, improving
mixing within the tanks, redesign of pressure zones for better interconnectivity,
changing pumping schedules to improve stored water turnover, or installation
of new water quality monitoring stations (Wilczak et al., 1996, Odell
et al., 1996; AWWA 2006a).
Dangerous Water Contaminants
is nitrification and how does it impact water quality? Nitrification is
a microbial process by which ammonia is sequentially oxidized to nitrite
and nitrate ions. Nitrification causes depletion of chloramine disinfectant
thus allowing bacterial regrowth. Every utility using chloramine needs
to assess nitrification potential and implement proper control measures.
Nitrite and nitrate ions produced due to nitrification are of no significance
to SFPUC. Other impacts of nitrification may include some decrease in
alkalinity, pH, and dissolved oxygen (Wilczak et al., 1996; Kirmeyer et
al. 2004). Nitrification is a utility operational issue and does not post
any health concerns. Nitrification results from metabolism and growth
of harmless non-pathogenic nitrifying bacteria that are ubiquitous in
soils and water. Utilities implement operational control measures, including
decreased water age and enhanced monitoring to limit the extent of nitrification
After this optimization period, the customers benefit from fresher water
that was stored for a shorter period of time in the distribution system.
SFPUC has implemented a vigorous nitrification monitoring and control
program and has been successful in controlling the nitrifying bacteria.