Even with 15 percent of Americans getting their drinking water from private wells, U.S. public water systems deliver more than 44 billion gallons of water every day to homes, schools, hospitals, and businesses. The majority of this water originates from surface water sources, such as lakes and rivers. Groundwater pumped from wells provides the rest. Before it reaches your home or business, your water goes through a treatment process that removes bacteria, chemicals, and particulates to ensure you receive clean water for drinking, cooking, and bathing.
At the other end of the clean water cycle is what happens to water after you flush it down the drain or toilet. Instead of wastewater releasing directly into the environment, it typically enters the sewer system and treatment plant first, which removes waste and other contaminants.
Clean Drinking Water
Thanks to governing bodies such as the EPA, the United States as a whole has some of the cleanest, safest drinking water in the world. Of course, the U.S. is also a country that allows states great autonomy, so water quality from state to state, and even city to city, varies dramatically. Even so, it must still meet EPA regulations.
Even with these guidelines, however, water contamination may occur, whether because the source becomes contaminated or something goes wrong in the distribution system after the water undergoes treatment.
Common Contaminants Found in Drinking Water
24th Street Water Treatment Plant (Source: City of Phoenix Water Services Department)
A contaminant is any substance, human-made or naturally occurring, that makes water unsafe to drink or use. Many of these are easily discernible by sight or taste, or even scent. Others, though, are only discovered after testing, and if left untreated, may cause disease.
Common natural contaminants include:
- Arsenic
- Bacteria
- Fertilizers
- Insecticides
- Lead
- Mercury
- Parasites
- Protozoa
- Viruses
Contamination occurs for a variety of reasons, including land use and practices, sewer overflows, manufacturing processes, or the release of wastewater. An improperly maintained water distribution system may also cause contamination.
The results of drinking contaminated water vary according to the person’s age and general health, as well as the contaminant in question. Those who are most susceptible include infants and young children, the elderly, pregnant women, and anyone with a compromised immune system. Common health issues include neurological disorders, gastrointestinal illness, and reproductive problems.
EPA Standards
The Environmental Protection Agency (EPA) is the department tasked with ensuring Americans enjoy clean air and drinking water. In addition, each state has its own agency overseeing these same issues. In Arizona, this is the Department of Environmental Quality (ADEQ). Both agencies identify harmful contaminants, setting standards that dictate maximum contaminant levels for safety.
Agencies divide contaminants into two categories: acute and chronic. Acute contaminants are defined as having adverse health effects within a certain number of hours or days after exposure. Chronic contaminants are those that require prolonged exposure before a person experiences adverse effects. Maximum safety levels for chronic contaminants are determined on a “lifetime” exposure. The EPA defines lifetime exposure as consuming two liters of water per day for 70 years.
Some people are more susceptible to certain contaminants, particularly those with a weakened immune system, such as children. This is particularly true with microbial contaminants, such as Cryptosporidium, as well as nitrates and lead. If the company supplying your water informs you that your water has elevated levels of nitrates or lead, and you have a baby younger than six months old, talk to your pediatrician about using an alternate source for drinking water.
The Water Treatment Process
Before water enters a storage facility, it goes through a four-step treatment process to ensure it is safe to drink.
Diagram courtesy of the EPA (Source: www.cdc.gov)
Step One: Coagulation and Flocculation
In this first step, positively charged chemicals enter the water to neutralize the negative charge of dissolved particles such as dirt. The positive and negative particles combine, forming larger particles known as floc.
Step Two: Sedimentation
In step two, the increased weight and size of the floc particles causes them to settle to the bottom of the water supply. This is called sedimentation.
Step Three: Filtration
With the floc at the bottom of the water supply, the clear water above passes through the filtration system, typically comprised of sand, gravel, and charcoal. The varying size and composition of these layers allow more effective removal of particles and other contaminants.
Step Four: Disinfection
Once filtration ends, the water treatment plant adds a disinfectant, such as chlorine or chloramines, to destroy any remaining bacteria, parasites, or viruses. This also protects water as it moves through the distribution system and into homes and businesses.
These steps may vary somewhat from location to location, as well as by the water source. For example, areas that receive their water from surface sources require greater filtration due to the increased contaminants found in rivers, lakes, and streams.
Lead in the Water
Typically, lead enters drinking water through the distribution system’s pipes. You find it most often when the source water is either low in mineral content or highly acidic, which tends to corrode the pipes. You also see this when the pipes themselves have lead solder, or brass and chrome-plated brass fixtures (more commonly seen in homes built before 1986).
The maximum amount of lead content across pipes, fittings, and fixtures is 0.25 percent, and only 0.20 percent for solder and flux, as per the Safe Drinking Water Act (SDWA). The EPA addressed corrosion leading to lead-contaminated drinking water with the Lead and Copper Rule. This rule requires utility companies to ensure water entering the system is less corrosive.
Different Areas, Different Issues
Different parts of the country experience different issues with their drinking water. For example, in the western part of the country, treatment plants often include a desalination step in their treatment process, as seawater and brackish groundwater have high saline content.
In agricultural areas, nitrate levels are higher due to the fertilizers, manure storage, and septic systems common in farming activities. High nitrate levels are especially dangerous for infants, so water treatment facilities take extra measures, such as ion exchange, to remove it.
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