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Copyright © 2005-2006 Environmental Technical Group, Inc.
Advanced Water
Continuous chlorination can be an effective method for disinfection of drinking water. It also can
be one step in the process of removing iron, manganese or hydrogen sulfide. Continuous
chlorination should not be a substitute for a sanitary water supply. Protecting the water supply
from contamination should be the primary goal for assuring good water quality. Continuous
chlorination can be a costly and complex treatment process and is often only considered after
other options are exhausted. This guide discusses the principles, processes and requirements of
continuous chlorination systems for the domestic (household) user.

What contaminants does continuous chlorination remove from water?
Purification of drinking water containing pathogenic (disease-causing) organisms requires
disinfection treatment. Disinfection of drinking water destroys pathogenic bacteria, nuisance
bacteria, viruses and other microorganisms, to produce a drinking water considered by public
health officials to be essentially pathogen free. Chlorination is the most commonly used method
for drinking water disinfection. Chlorine will oxidize iron and manganese so they can be filtered
out and also oxidize hydrogen sulfide to reduce nuisance odors.

Water used for drinking and cooking should be free of pathogenic organisms that can lead to
illnesses such as typhoid fever, dysentery, infectious hepatitis and gastroenteritis. Pathogenic
bacteria and viruses can be transmitted to humans by several routes, including contaminated
drinking water supplies. Concentrated human and/or livestock populations near wells may result
in contaminated water supplies. Contamination can also occur during or after well construction or
repair, or flooding. Water can also be contaminated with naturally-occurring nuisance organisms
such as iron bacteria, slime bacteria and sulfate-reducing bacteria. Disinfection by a process
such as continuous chlorination is necessary for surface water supplies. It also is used to treat
ongoing bacterial contamination and the process is similar to that used by public water utilities.
Shock chlorination is used for new wells or after well repairs and is recommended for treating
non-recurring bacterial contamination.

What contaminants are not removed by continuous chlorination?
Chlorine will not remove nitrate from water. Chlorination will not remove heavy metals, calcium
and magnesium (hard water minerals), fluoride, and many other compounds. The concentration
of chlorine typically applied for disinfection will not adequately destroy protozoan cysts such as
Giardia and Cryptosporidium. These contaminants are not normally found in  groundwater but
may be present in contaminated surface water. The effectiveness of removal or destruction of
microbial contaminants by chlorination depends on numerous factors as discussed later in this
guide under Treatment Principles. Often, chlorination is used to oxidize contaminants such as
iron and manganese to form precipitates; then a filter is used for removal of these precipitates.

No one piece of treatment equipment manages all contaminants. All treatment methods have
limitations and often situations require a combination of treatment processes to effectively treat
the water.

Water Testing
Regardless of the water treatment system being considered, the water first should be tested to
determine what substances are present. Public water systems routinely are tested for
contaminants. Water utilities are required to publish Consumer Confidence Reports (CCRs),
which inform consumers on the source of the water, contaminants that are present, potential
health effects of those contaminants and methods of treatment used by the utility. Depending on
the number of customers served by the utility, CCRs may be mailed, published in newspapers or
posted on the Internet. A copy of the CCR can be obtained by contacting the local water utility.
Public supplies must conform to federal standards established by the Safe Drinking Water Act. If
contaminants exceed the Maximum Contaminant Level (MCL), the water must be treated to
correct the problem and/or another source of water suitable for drinking must be provided.

In contrast, monitoring of private water systems is the responsibility of the homeowner.
Therefore, contamination is more likely to go undetected in a private water supply. Knowledge of
what contaminants may be present in the water should guide the testing, since it is not
economically feasible to test for all possible contaminants. It is essential to know what
contaminants are present, their quantities and reasons for their removal (i.e., to reduce
contaminants posing health risks, to remove tastes or odors, etc.) before selecting treatment
methods or equipment.  Private well owners should have their drinking water tested for
bacteriological contamination at least once each year and after any repair or improvements in
the well.

Coliform bacteria testing is used to indicate the presence of disease-causing bacteria in drinking
water. Coliform bacteria are organisms found in soil and in the intestinal tract of warm-blooded
animals. Coliform bacteria are not necessarily pathogenic, but are indicators of possible
contamination (For example, if the water is positive for coliform bacteria, it indicates the possibility
of contamination by soil or waste from humans or animals, which may contain pathogenic
organisms). Laboratory tests for coliform bacterial may be performed by use of the MPN (most
probable number), MF (membrane filter) method, or Colilert® method. If no coliform bacteria are
detected, results from the MPN method will be reported as "less than 2.2." Results from the MF
method can be expressed as either text ("present" or "absent"), or as the detected number of
bacteria. Results from the Colilert® method is expressed as either "present" or "absent."
Coliform presence in a drinking water sample does not necessarily mean the water is unsafe to
drink. Since the test is a screening tool, a positive result should initiate additional testing,
perhaps at different locations (well, pressure tank, etc.) in order to identify the source of the
contamination. If the results reported show high coliform numbers, there is most likely
considerable contamination and the water should not be consumed until the source of
contamination is identified and eliminated, and/or the water is purified. In such situations, further
water sample analysis for fecal coliform or E. coli should be initiated.

Treatment Principles
The best option for assuring good water quality is protecting the water source from contamination
in the first place. If your water supply does become contaminated, removing the source of
contamination is the ideal solution. Chlorination should not be a substitute for a sanitary water
supply. Because of the cost and management requirements of continuous chlorination, many
water treatment professionals will suggest drilling a new well (or in some cases moving the source
of contamination, such as a septic tank) as a preferable option over continuous chlorination.
The disinfecting effectiveness of chlorine depends on the concentration in the water, the amount
of time the available chlorine is in contact with the water prior to use (contact time), the water
temperature, water pH and the characteristics of the contaminants and water supply. When
chlorine is added to water it reacts with microorganisms, certain chemicals, plant material, and
compounds that can cause taste, odor or color in the water. These components "tie up" some of
the chlorine and this is called the chlorine demand. The chlorine that does not react with these
contaminants is free, or residual, chlorine. The breakpoint is that concentration of chlorine that
just meets the chlorine demand so that a higher concentration would allow for some residual
chlorine. It is important to have enough chlorine in the water to meet the chlorine demand and
allow for residual disinfection. Test kits are available from plumbing or water supply equipment
dealers for testing chlorine in private systems; be certain the kit you purchase tests free chlorine,
not total chlorine.

The concentration of free chlorine necessary for adequate disinfection is system-dependent; the
chlorine concentration is depended on the amount and type of contamination present, water pH
and temperature, etc. Consult your water treatment specialist for guidance on proper free
chorine residual concentration for your situation. Household chlorination systems may provide a
higher free chlorine concentration than the typical 0.3 - 0.5 ppm (parts per million) concentration
used for chlorination of public water supplies. The distribution system of a public water system
provides a much longer contact time than a household plumbing system so a lower concentration
may be used for disinfection. Piping in home water systems generally provides very limited
contact time for chlorination since the time between the pump and the nearest faucet is usually
one minute or less. A coil of plastic pipe may be used to increase the contact time within the
system. The length of pipe needed depends on the flow rate and the pipe diameter; consult a
water treatment professional for determining the length needed for your system. Also, other
features such as storage tanks with baffles or mixers may be installed by professionals to
increase contact time so lower chlorine concentrations typical of public systems can be used.
Other systems increase contact time by chlorinating the water in the well before it is pumped to
the house. For information on different types of chlorination systems see the discussion on
treatment equipment later in this guide.

The reaction of chlorine with trace concentration of naturally occurring organic matter can
produce compounds such as trihalomethanes (THMs) as by-products. These disinfection
by-products may increase the risk of certain cancers. The EPA mandates that public water
systems have less than 80 parts per billion (ppb) of THMs in their treated water. Activated carbon
filtration can be effective in removing chlorine and some disinfection by-products from drinking
water. Activated carbon filters will need periodic replacement according to manufacturer's
instructions. See NebGuide G03-1489 Drinking Water Treatment: Activated Carbon Filtration for
further information on the activated carbon filtration process. THMs are primarily a concern for
surface water supplies. Groundwater rarely has high levels of organic matter so exposure to
THMs from chlorination of private well water is generally low. Also, exposure can vary with
season, contact time and water chemistry. Though there is a risk associated with consuming
THMs in chlorinated water, the health risks associated with consuming pathogen-contaminated
water are far greater.
Chlorine concentrations used for disinfection in water are not toxic to humans or animals. The
concentration can be high enough, however, to create a taste or odor that some people find
objectionable. Activated carbon filtration following chlorination may be used to remove the taste
and odor.

Chlorine is available in dry form as either a powder or pellets (calcium hypochlorite) or in liquid
form (sodium hypochlorite). Both forms of chlorine must be stored in accordance with the
manufacturers' recommendations for safety purposes and to maintain the chemical integrity of
the product. Chlorine gas as used by public utilities is too dangerous and costly for household

There are three common types of chlorinators for continuous chlorination of a home drinking
water supply: a chemical feed pump, an injection device and a tablet chlorinator. Because the
effectiveness of the disinfection is a function of contact time, in each type of chlorinator the
chlorine should be introduced into the water as close to the source as possible, often in
conjuction with one or more large tanks (contact tanks). This will allow the chlorine a longer
contact time with the water.

Figure 1 shows a chemical feed pump chlorinator. A fixed amount of chlorine solution is delivered
with each pump discharge stroke. The amount delivered can be adjusted by changing the length
of the discharge stroke, the speed of the pump, or the running time of the pump. The feed pump
should be wired to the water pump pressure switch so that the chemical pump operates only
when the water pump is operating. The system should also have a device to indicate when the
chlorine solution supply is low or if the chemical pump fails.

Selection Requirements
Federal, state or local laws do not regulate continuous chlorination home systems. The industry
is self-regulated. The NSF (formerly known as the National Sanitation Foundation) and the Water
Quality Association (WQA) evaluate performance, construction, advertising and operation
manual information. The NSF program establishes performance standards that must be met for
endorsement and certification. The WQA program uses the same NSF standards and provides
equivalent American National Standards Institute (ANSI) accredited product certifications. WQA
certified products carry the Water Quality Association Gold Seal. Though these certifications and
validations should not be the only criteria for choosing a continuous chlorination system, they are
helpful to ensure effectiveness of the system.

Drinking water treatment using continuous chlorination disinfects a water supply. It destroys
pathogenic bacteria, nuisance bacteria, viruses, some parasites and other microorganisms. It
also oxidizes iron and manganese so they can be filtered out, and oxidizes hydrogen sulfide in
order to reduce nuisance odors. Continuous chlorination is a complex and relatively expensive
treatment process. It requires continuous monitoring and knowledgeable management. Using
continuous chlorination for control of bacteria should not be considered without consulting a
professional and fully exploring other options such as drilling a new well or eliminating the source
of contamination.