If you ever have the opportunity to tour a good public drinking water treatment facility, you will see that a number of different steps are in place to remove or reduce impurities large and small. The steps that are taken depend, primarily, on the quality of the source, although municipal finances do sometimes come into play.
Above ground sources, such as rivers, lakes or reservoirs require the most steps. Illness-causing pathogens, such as bacteria and viruses, can thrive in above-ground sources, particularly during the warmer months of the years.
In order to avoid outbreaks of waterborne illnesses, which is the term used by health care professionals to describe them, facilities use disinfectants, such as chloramines or bromine. UV light may be used, as well as exposure to ozone or oxygen. Whatever the facility believes is necessary to prevent the spread of illness.
But, that's not the first step for an above ground source. Large particles, such as mud, dirt, rocks and sticks, are removed using a wire mesh. The mesh can become clogged. Keeping it clear is one of the jobs performed by the facility's employees.
Drinking water treatment and wastewater treatment have some things in common. Both facilities can make use of a reverse osmosis step, although the process is expensive and is usually reserved for specific contaminants. Lead, for example, is one of the hazardous compounds that can be removed through the use of reverse osmosis.
Wastewater facilities use a settling process to separate solid waste from liquids. Eventually, the solid particles are formed into pellets and are sometimes used as fertilizer, although many farmers are put off by the smell.
Once the cleaning process is completed, the wastewater is returned to a river or ocean. The EPA hopes that the processes used will protect fish and other wildlife, as well as people living downstream.
When it comes to drinking water treatment facilities, the EPA hopes that the necessary steps are taken to prevent outbreaks of waterborne illness, which is a goal that most facilities are able to achieve. The EPA has set allowable limits for other contaminants, such as lead and chemical disinfectants.
Facilities are required to adhere to those limits. Although former EPA employees have said that enforcing the limits is next to impossible, because of limited staffing. Warnings are issued, but not always followed up on.
One thing that a public drinking water treatment cannot do, according to the EPA, is address the issue of cyst contaminants. They say that cysts may be present at any time, but contamination is most common during spring and summer.
Cysts are something like bacteria, but they are resistant to all known disinfection methods, other than boiling. They are most common in areas near farms, where run-off is a problem.
A public facility cannot address the issue of cysts, because they are too small. The EPA recommends home drinking water treatment systems for some individuals, because of the risk of cysts. Many health experts recommend home systems for everyone. There's only so much that a big facility can do.