Science of Water : Concepts and Applications

Water Pollution 205
and that is that), if we were to inspect the contents, a few possibilities might present themselves.
The contents might appear cloudy or colored (making us think that the water is not fi t to drink). The
contents might look fi ne, but carry the prevalent odor of chlorine. Most often, when we take the
time to look at water drawn from the tap, it simply looks like water and we drink it or use it to cook
with, or whatever.
The fact is, typically a glass of treated water is a chemical cocktail (Kay, 1996). While water utilities
in communities seek to protect the public health by treating raw water with certain chemicals,
what they are in essence doing is providing us a drinking water product that is a mixture of various
treatment chemicals and their by-products. For example, the water treatment facility typically adds
chlorine to disinfect; chlorine can produce contaminants. Another concoction is formed when ammonia
is added to disinfect. Alum and polymers are added to the water to settle out various contaminants.
The water distribution system and appurtenances also need to be protected to prevent pipe corrosion or
soften water, so the water treatment facility adds caustic soda, ferric chloride, and lime, which in turn
work to increase the aluminum, sulfates, and salts in the water. Thus, when we hold that glass of water
before us, and we perceive what appears to be a full glass of crystal clear, refreshing water—what we
really see is a concoction of many chemicals mixed with water, forming the chemical cocktail.
The most common chemical additives used in water treatment are chlorine, fl uorides, and
fl occulants. Because we have already discussed fl uorides, our discussion in the following sections is
on the by-products of chlorine and fl occulant additives.
BY-PRODUCTS OF CHLORINE
To lessen the potential impact of that water cocktail, the biggest challenge today is to make sure the
old standby—chlorine—will not produce as many new contaminants as it destroys. At the present
time, weighing the balance of the argument, arguing against chlorine and the chlorination process
is diffi cult. Since 1908, chlorine has been used in the United States to kill off microorganisms that
spread cholera, typhoid fever, and other waterborne diseases. However, in the 1970s, scientists discovered
that while chlorine does not seem to cause cancer in lab animals, it can—in the water treatment
process—create a whole list of by-products that do. The by-products of chlorine—organic
hydrocarbons called trihalomethanes (usually discussed as total trihalomethanes or TTHMs)—
present the biggest health concern.
The USEPA classifi es three of these trihalomethanes by-products—chloroform, bromoform,
and bromodichloromethane—as probable human carcinogens. The fourth, dibromochloromethane,
is classifi ed as a possible human carcinogen.
The USEPA set the fi rst trihalomethane limits in 1979. Most water companies met these standards
initially, but the standards were tightened after the 1996 Safe Drinking Water Act (SDWA)
Amendments. The USEPA is continuously studying the need to regulate other cancer-causing contaminants,
including haloacetic acids (HAAs) also produced by chlorination.
Most people concerned with protecting public health applaud the USEPA’s efforts in regulating
water additives and disinfection by-products. However, some of those in the water treatment
and supply business express concern. A common concern often heard from water utilities having
a tough time balancing the use of chlorine without going over the regulated limits revolves around
the necessity of meeting regulatory requirements by lowering chlorine amounts to meet by- products
standards, and at the same time ensuring that all the pathogenic microorganisms are killed off.
Many make the strong argument that while no proven case exists that disinfection by-products
cause cancer in humans, many cases—a whole history of cases—show that if we do not chlorinate
water, people get sick and sometimes die from waterborne diseases.
Because chlorine and chlorination are now prompting regulatory pressure and compliance with
new, demanding regulations, many water treatment facilities are looking for options. Choosing
alternative disinfection chemical processes is feeding a growing business enterprise. One alternative
that is currently being given widespread consideration in the United States is ozonation, which uses