Inorganic Compounds
Metal and metalloid positive ions: Some of these ions (lead, mercury, and arsenic) are dangerous at extremely low concentrations and can be introduced into drinking water either though natural processes or as a result of human activity. Other ions in this group (for example, calcium, magnesium, sodium, and potassium) are essential to human health – in the correct amounts.
Calcium and magnesium are interesting ions: Although their presence in drinking water is actually a health benefit, they are the prime culprits in most hard water, and are considered undesirable contaminants by those who must live with scaly deposits of calcium carbonate on their faucets (and in their pipes and water heaters) or who can not get their soap to lather.
Negative ions: As with the positive ions, some of these negative ions are necessary for life as long as they are in proper concentrations (chloride and carbonate); while others can be dangerous to health at moderate concentrations (nitrates and nitrites – look at the ingredients in the next slice of ham, bacon, or hot dog you eat); and still others are dangerous at even small concentrations (cyanide). Regarding some, controversy remains high. Flouride, for example, which has been added to drinking water to lessen tooth decay, may actually do more harm than good, particularly where children are concerned.
Radon: Radon is a radioactive gas, which comes from the natural breakdown (radioactive decay) of radium, which is itself a product of uranium decay. The primary source of radon in homes is from the underlying soil and bedrock. However, an additional source could be the water supply, particularly if a private well or a small community water system serves the house.
Organic Compounds
These compounds all contain the element Carbon. Although there are many exceptions, naturally occurring organic compounds (sugars, proteins, types of alcohol, etc.) are synthesized in the cells of living organisms, or like raw petroleum and coal, formed by natural processes acting on the organic chemicals left behind by previously living organisms.
Synthetic Organic Chemicals
Organic chemicals can also be synthesized in laboratories and by chemical companies. A growing number of these synthetic organic compounds are being produced. They can include pesticides used in agriculture, plastics, synthetic fabrics, dyes, gasoline additives like MTBE, solvents like carbon tetrachloride, and many other chemicals.
Many synthetic organic chemicals, like benzene, carbon tetrachloride, and vinyl chloride, vaporize easily in air and are grouped under the category of volatile organic chemicals (VOCs). Methyl tertiary butyl ether (MTBE) is a common synthetic organic chemical used for a number of years as a gasoline additive. In January 2000 it received national notoriety on CBS’ 60 Minutes because of its ability to contaminate water supplies after leaking from storage tanks.
The potential for water contamination by synthetic organic chemicals can be understood by the fact that Denver Water (the company that supplies municipal water to much of the metro Denver area) tests for 54 VOCs, 73 pesticides, 25 chemicals classified as synthetic organic compounds, and 7 chemicals classified as non-specific organics. Nearly all of these chemicals tested below the levels of detectability. It is somewhat disconcerting to realize that Denver water tests for only 150 or so of the thousands of synthetic organic chemicals.
These are not nice chemicals to have in your water, many of them are presumed to increase the risk of various cancers in humans, often after many years of low-level exposure; others may affect the nervous system. Some researchers are reporting that yet other synthetic chemicals can cause hormonal disruptions. Most laboratory tests of the effects of these chemicals are done using a single chemical, but there may be several organic contaminants together in a water source. Scientists are just beginning to realize that exposure to multiple, organic chemicals seems to increase the risk of health problems much more than any of the chemicals would separately.
Trihalomethanes
There is a class of organic compounds that is important because their formation and presence in drinking water is a direct result of the most common and economical process used to kill harmful pathogens, chlorination. This chemical group is the trihalomethanes (THMs). THMs are formed when the chlorine that is added to water interacts with organic material also in the water, like leaf fragments, etc. The level of THMs in water is usually greater in water systems where surface water is the source, and levels typically vary seasonally with the organic content of the source water supply.
Chloroform is usually the most common THM, and in Denver for instance, it varies from about 10 micrograms per liter in the winter to about 50 micrograms per liter in the summer with an average around 20-25 micrograms per liter. These levels are well below the EPA’s Maximum Contaminant Level (MCL) of 100 micrograms per liter. However, drinking water with THM levels below 100 microgram per liter over a 40-50 year period may increase the risk of certain cancers. Evidence has also been reported that disinfection byproducts can cause adverse reproductive outcomes.
Materials Suspended in Water:
Of the extremely large number of things that can possibly be suspended in water, only those that are dangerous to health or that affect drinking water quality will be listed here. If there are enough tiny particles suspended in water it becomes cloudy or turbid. Light bounces off the suspended particles giving the water a milky or muddy appearance. Gasses dissolved in water can also cause turbidity if they begin to come out of solution or “degas” (like the bubbles that form when a carbonated drink is opened). Gas bubbles will eventually rise to the surface and disappear – the water will clear, other materials suspended in water neither rise nor settle, so the water does not clear.
Pathogens
Pathogens are disease-causing organisms. Note: exposure to the disease causing organisms discussed below (E. coli, cryptosporidia, giardia, etc.) can come from sources other than one’s drinking water. For instance, exposure can come from eating contaminated food, or from swimming in contaminated water. Additionally, although according to the EPA, viruses can cause “gastrointestinal illness (e.g., diarrhea, vomiting, cramps),” I have not read of specific outbreaks of virus-caused diseases.
Bacteria
Over one hundred years ago, cholera (caused by Vibrio cholera) and typhoid fever (caused by Salmonella typhi) were responsible for epidemics (caused by drinking contaminated water) that killed many thousands of people. Today, in most parts of the world, because of chlorination and other water purification processes, we do not usually hear about cholera outbreaks unless an accident or natural disaster has disabled water purification plants.
Today in the US, the pathogenic bacterial contaminant most often encountered is fecal bacteria, or E. coli, which enters the water supply via human or animal wastes. The EPA regulates the maximum allowable levels for these bacteria in drinking water and most people either do not encounter these bacteria in their drinking water or do not get sick. The article, “Tap Water at Risk” by the Houston Chronicle, reported that in the USA between 1994 and 1995, there were 3,641 water purification utilities in the US that reported violating the federal health standards for fecal bacteria contamination. These utilities together served 11.9 million people.
Protozoans – Cryptosporidia and giardia.
These are one-celled organisms, both of which form dormant cyst stages that are resistant to typical levels of chlorination, cause gastrointestinal disease, and are prevalent in the environment. According to EPA, May 1996: “Cryptosporidium has been found in nearly all surface waters that have been tested nationwide. As water systems monitor for Cryptosporidium, the likelihood exists that it will be detected occasionally at low levels in finished water derived from surface water sources. Cryptosporidium oocysts are very resistant to disinfection, and even a well-operated water system cannot ensure that drinking water will be completely free of this parasite.” According to the Center for Disease Control and Prevention: “Cryptosporidium parvum has been recognized as a human pathogen since 1976. In people with normally functioning immune systems, Cryptosporidiosis is manifested as an acute, self-limiting diarrheal illness lasting 7 to 14 days and it is often accompanied by nausea, abdominal cramps, and low-grade fever.” For people with compromised immune systems an infection can be fatal.
Asbestos
Asbestos forms minute fibers in the environment. You usually hear about exposure to airborne asbestos causing disease. Asbestos fibers can also be present in water and the EPA regulates it because asbestos exposure from water has been linked to an increase in the risk of certain cancers.
Other Suspended Solids
Unless the materials in the water are themselves dangerous, suspended solids are typically a nuisance rather than hazardous. Suspended materials in the water however, can interact with the disinfection processes, making them less effective. Water professionals also use turbidity of the finished water as an indicator of its quality. If the purification process is letting enough solids through that the water is cloudy, there is a chance that some of the “stuff” contributing to the turbidity is harmful.
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