|
|
Trihalomethanes (THMs)
Frequently Asked Questions
What are trihalomethanes?
Trihalomethanes (THMs) are a byproduct of the water
treatment process. They are formed when natural organic material, such
as the decaying vegetation commonly found in lakes and reservoirs, reacts
with chlorine used to treat the water. This reaction produces “disinfection
by-products,” the most common of which are THMs. The water district
conducts tests every month to monitor the levels of total THMs in both
treated and source water, and reports these levels to the state department
of health. The district also posts the results of our water
quality analysis and issues a quarterly water quality report that
is available to the public.
Top of page
What are the THM levels in the water the district provides?
You can view the water district’s most recent lab
data. First choose the monthly lab report you wish to view. THM
levels are reported as "total trihalomethanes" in (mg/L) and
are found in the second data grouping under Primary Standards - Mandatory
Health-Related Standards. Since 1993, levels of THM measured in treated
water range from .040-.100 mg/L. During the drought years of 1987-1992,
levels tended to be higher (.080-.100 mg/L). This is because the drought
condition increased levels of salt water intrusion and agricultural
runoff in the source water from the Sacramento-San Joaquin Delta.
Top of page
Why do you use chlorine if it creates these byproducts?
Chlorine has been used to disinfect water for almost a century due to
its effectiveness at killing bacteria and viruses in water. There is
no question that its use has been a huge public health benefit in largely
eliminating plagues such as cholera and typhoid and reducing the incidence
of intestinal illness and other health problems caused by waterborne
germs. In 1974, drinking water professionals recognized the need to
modify traditional chlorine treatment processes due to advances in knowledge
about disinfection byproducts and their health impacts. In 1979, the
U.S. Environmental Protection Agency adopted a regulated limit on the
amount of THMs allowable in drinking water, of 100 parts per billion.
The water district produces water with the least amount of THMs possible,
by doing such things as delaying chlorination (which reduces the formation
of byproducts by limiting the time that chlorine is in contact with
organic materials), switching source water when levels of organic material
are high, enhancing coagulation, which improves the removal of organic
materials before the treatment process; and using chloramine instead
of chlorine for residual disinfection.
Top of page
What can you do to get these out of the water?
The water district is currently upgrading all three of its drinking
water treatment plants in order to allow for new and improved methods
of treatment that will further reduce the levels of THMs in treated
water that we provide to the county. This will be accomplished by further
delaying chlorination and enhancing coagulation, and eventually by switching
to ozonation as the primary disinfection method instead of chlorination.
This $150 million capital improvement project is scheduled to be completed
in 2005. The district is examining ways that the project could be accelerated.
Another important factor in reducing the amount of THMs
in the treated water we provide is the need to improve the quality of
the source water. Water imported from the Sacramento-San Joaquin Delta
currently experiences salt water contamination and has high levels of
organic compounds from agricultural drainage. These salts and organic
compounds form THMs during the treatment process. The delta serves as
the primary source of drinking water for some 20 million Californians.
The district is participating in the CALFED process, a state-federal
program to restore the delta and improve the quality of the water that
we import. Taxpayer support of CALFED initiatives will be critical to
the success of this effort.
Top of page
I am pregnant. Should I stop drinking tap water?
Pregnant women should talk to their physician for advice. It is important
that pregnant women continue to drink sufficient water according to
their doctor’s recommendations. Health officials are not recommending
that pregnant women stop drinking their tap water. If you are concerned
about the safety of your tap water, you have several options. These
are explained in greater detail here.
Top of page
Are there additional exposures to THMs associated with showering or
bathing?
THMs can evaporate and be inhaled while showering, however, the EPA
has determined that this exposure is minimal compared to that from consumption.
Top of page
Is the water safe for the general public to drink?
Yes, the water is safe for the general population to drink. If you have
a medical condition that suppresses your immune system, or if you are
worried about the quality of your tap water, you can consult your doctor
for recommendations or follow the advice given above.
Top of page
Where can I get more information?
Questions on tap water quality:
- California Department of Health Services, (916)
323-4344 or (510) 450-3818 for questions about the recent study
- US Environmental Protection Agency Safe Drinking Water
Hotline 800-426-4791
- Your
water retail company
- Santa Clara Valley Water District, (408) 265-2600
- Environmental Protection Agency’s Safe Drinking
Water Hotline, 800-426-4791
Questions on the health impacts relating to these
issues:
- Dr. Martin Fenstersheib, County Health Officer,
(408) 885-4214
For copies of literature on water supply, home treatment
systems, and other water quality issues:
- Santa Clara Valley Water District Public Information
Office at (408) 265-2607 ext. 2238
For information on home water treatment devices:
For information on bottled water regulations and quality:
- Wayland Ho, Food and Drug Investigator, California
Department of Health Services, Food and Drug Branch, 100 Paseo de
San Antonio, Room 304, San Jose, CA 95113
- International Bottled Water Association, 113 North
Henry Street, Alexandria, VA, 22314, (703) 683-5213
|
|
|
