Considering the fact that our bodies are mostly made from water, it's easy to see why we need to consume so much of it per day (about 3 liters--more, if you exert yourself to any extent). In fact, without access to clean, drinkable water, we would soon die.
To put this in a different light: we can live without food for days and even weeks (depending on our age, health status and body weight), but we will die within a relatively short time without access to drinkable water. The word "drinkable" is of key importance. Having access to ocean water (when maybe stranded on some island or falling off a ship and left behind), for example, would be useless since ocean water is too salty for our bodies to process safely.
By the same token, heavily polluted, chemically treated (such as with chlorine, fluoride or chloramines, a combination of chlorine and ammonia) or dirty water (containing dirt, sand or disease-promoting microorganisms) might be equally dangerous. In the past, naturally-dirty and microbe-infested water were the main problems--but those contaminants were easily removed either with simple filtration (using a fine mesh or cloth) or by simply boiling it (which killed most microbes in question).
Today, however, the issues relating to polluted water are more complex and difficult to deal with than in the past. This problem has, ironically, been further exacerbated by the potentially toxic chemicals deliberately added to water in order to "treat" such. Yes, chlorine and fluoride will indeed kill many microbes, but they can also be toxic to human beings, especially when consumed regularly.
Fluoride, like lead and mercury, can accumulate in the body (usually the bones), meaning that its effects not only linger on but should be measured in terms of how much of it you consume, not just daily, but over a life-time. For this and other reasons, the less fluoride you are exposed to, the better; more importantly, at this time no one knows for sure at what point built-up fluoride in your body leads to diseases--most notably, cancer.
The chemicals that municipal water treatment facilities add to your water, though, are only a small part of the serious problems with the water that you drink, cook with, bathe in and wash your clothes and dishes in. Add to that the many toxic substances that are ending up, naturally or from out-of-control pollution, in your water--and this also goes for water from wells and the hitherto-pristine water aquifers that have been buried deep beneath the earth for ages (until man found ways to seriously pollute them on behalf of the oil, mining and radioactive-materials industries).
Just What Kind of Poisons Should I Expect to Find in My Water?
Alas, the list of toxic things that your water may potentially contain keeps getting bigger and bigger each year. Sadly, no one (not even the EPA) can answer this question with complete certainty, mostly because there are many new chemicals being added each year; also, many of these toxic things are finding their way in your water through accidental leaching or criminally-minded dumping acts.
Here is a short list of what is commonly found in American water sources:
Radioactive materials and substances
Volatile organic compounds (VOCs)
By-products of chlorination
Municipal water treatment plant additives
Potentially toxic (when consumed excessively or, for some of these, if at all) metals
While the government does keep track of most of these toxins, there are many other toxic substances (especially those illegally dumped, accidentally created by unforeseen chemical interaction, or derived from natural sources, which then leach into water sources) which are not being closely monitored, even though they may be in the water that you use every day.
You must also realize that just because the government knows and monitors some of these toxins doesn't mean that they are filtering or purifying them out of your water; in fact, thorough filtering and purification of public water isn't officially mandated--instead, water management authorities are supposed to officially inform the public of any significant impurities so that the public can either avoid use of said water or take action on their own.
In other words, it's your responsibility, as a citizen and taxpayer, to protect yourself from toxins in your water--and that includes the chemicals meant to treat the water for disease-inducing microorganisms. Accordingly, you are expected, even if you have not been informed by the government of all known or possible contaminants in your water, to filter and/or purify your water, as needed.
You may have, for example, been warned about high E. coli content in your water in the past (especially after a hurricane or some other unavoidable water-contamination event), for which boiling of water was likely recommended. In some parts of the country, citizens have also been advised against dangerously-high radioactive particles (alpha, beta, etc.) being detected in their water sources. In all these cases, citizens have been advised to take steps to either filter or purify their water--either that, or to forego using it.
What's the Difference Between Water Filtering & Purification?
Both filtering and purification involve putting water through some device or process which makes the water more fit for human use and consumption. Filtering your water, though, is generally simpler and cheaper. It generally involves letting the water pass through some filtering device (often containing granular activated carbon) meant to basically trap or "adsorb" relatively large particulates and substances (soil, dirt, metals, microorganisms & some high-viscosity chemicals).
These devices range from pitchers that let water drip through a filter (so that water may be consumed directly) to devices that attach to the water pipe under the sink. They also make a whole line of POU devices that may be taken on camping trips if having to take water from natural bodies of water on the way.
Water purification, however, involves actually treating the water, such as when chlorine, iodine or fluoride is added to water in order to kill disease-inducing microorganisms. This can also involve the use of UV light, which essentially does the same thing these chemicals do, although, unlike chemical treatments, this doesn't leave any potentially dangerous chemical residues after treatment.
Water purification can also involve extensive or sophisticated filtering processes/devices, such as may be used in whole-house water purification systems. In fact, such systems usually involve both processes--often necessary in order to be able to take out all potential contaminants. Such sophisticated systems/devices, for example, provide filtering for more minute or fine particles/substances; it can also involve such processes as reverse osmosis, distilling, UV radiation, and ionization.
How May Contaminated Water Negatively Affect My Health?
Most people are acquainted with waterborne diseases such as malaria, cholera, Shigellosis, etc. What these diseases have in common is the fact that microorganisms cause them. Although these diseases can be serious (potentially fatal), they are generally under control (for the most part) in developed countries. Things may be drastically different when it comes to developing countries.
When it comes to chemical or radiation-induced disease, though, things become much more complicated, and, to be blunt, much more serious. The problem is that this type of contamination is more likely to lead to chronic disease--i.e., disease that takes a long time to establish itself and may linger on for years (as opposed to disease that has quick, easy-to-identify repercussions and doesn't linger). Good examples of such diseases include cardiovascular disease, diabetes, cancer, autoimmune disorders, reproductive syndromes, developmental disorders, allergic reactions, etc.
The bottom line is that toxic contaminants may interfere with your body's ability to fight off disease, compromise the role of each of your organs, make it more difficult for cells to reproduce and function at peak capacity, impede or overwhelm your body's ability to cleanse your body of dangerous toxins, metals and biological intruders, and absorb the nutrients we all need to maintain good health. While we can't say for sure how much these ubiquitous contaminants are to blame for the rise in both morbidity and mortality of chronic disease, the fact that chronic diseases continue to get worse year by year is reason enough to express concern--hopefully, culminating in appropriate defensive action.
For your part, realize that any contaminant, especially if not naturally found therein, that ends up in your water (ostensibly, as a result of illegal dumping, derivatives of toxic mining/manufacturing processes, and unforeseen chemical interactions) most likely poses a threat to your health. Fortunately, many of the chemicals commonly found in water have already been identified as (or are suspected of) being disease-inducing; this is especially troubling for those substances thought to be mutagenic, teratogenic or carcinogenic.
By all means, strive to avoid these substances like the plague.
Even substances whose toxicity have been contested should be avoided, if at all possible. Glyphosate, fluoride, atrazine, neonicotinoids and pyriproxyfen are perfect examples. All these substances have been adamantly defended by their makers (and for-sale journalists) not because the charges against them are unsubstantiated or weak but because all of them have proven to be exceedingly profitable.
Accordingly, their makers have invested millions in slick, sleazy campaigns meant to cover up or downplay their toxicity. Don't fall for these shameful and horribly unethical tactics. These people are only looking out for their financial interests; in sharp contrast, what matters most to you and me is our health and the health of our fellow human beings.
In spite of some articles defending these chemicals, there is now substantial evidence for including them in the list of chemicals to avoid in your water. Here are some basic reasons to avoid each:
Glyphosate. This toxin, simply put, has been (and continues to be) over-used for too long. We know this because it is now being found in our food and water sources in ridiculously high amounts. A recent study has even found it in the chemistry of most Americans--meaning that it accumulates in the body. This nasty stuff is strongly suspected of being a carcinogen and of possibly being tied to the high cases of microcephaly in South America.
Fluoride. First of all, the fluoride that they dump into your water (a waste by-product of the mining/manufacturing industries) is not the pure fluoride most people think is being used. This poison, a known neurotoxin, was used as a rat poison in the past, was used by Nazis against Jews and other prisoners, and may not even impart any of the benefits (reduce cavities, save teeth, etc.) it is said to impart. By all means, look for fluoride-free toothpaste and filter/purify this chemical out of your water, if you can.
Atrazine. We need more short and long-term toxicity studies (not just using animals) on atrazine. Since it has never been proven to be safe, with adequate impartial studies involving humans for extended periods of time (involving 3 years or more), it shouldn't be in our water--period!
Neonicotinoids. These over-used, ubiquitous pesticides are responsible, according to mounting evidence, for the still-ongoing destruction of honey bees around the world. Both corporations and the US government have known this but, yet, out of concern for lost revenue (once the truth got out) they have continued to spray this garbage with impunity. This toxin has been so irresponsibly over-used (like glyphosate) that it can also be found in water in many places. Needless to say, this toxin needs to be completely banned immediately, while we have bees left to save . . . and, as an unimportant (to the government) after-thought, it is also probably harming us (if it is killing bees).
Pyriproxyfen. This stuff was irresponsibly dumped into the drinking water of Brazilians. Surprisingly (or maybe not so "surprisingly") incidence of microcephaly increased in the areas where this toxic water was served to the public (mostly without their knowledge). The for-sale press claimed that the Zika virus was to blame but, considering that the Zika virus never had this capacity, it's safe to say that this was classic BS from the highest (or should we say, "lowest") sources. Don't be surprised if the US government decides in the future to dump this larvicide into American waters (if they aren't doing so secretly already); shockingly, it's already being used in a variety of products (including carpet powders, foggers, shampoos, baits, pet collars, etc.) in the US.
The water that is coming to your house or that you find while hiking through the great outdoors is most likely contaminated--the only question is "how badly?" While what contaminants may be found in each sample of water may differ, the fact is that most of these contaminants pose significant health threats. This is especially true if the water sources near you are close to a garbage disposal facility, an illegal dumping site, a designated (or unofficial) hazardous waste location, manufacturing companies, mining operations, nuclear power plants, research labs, and military installations.
Actually, large urban communities (because they create so much human waste & manufactured refuse) themselves pose significant contamination threats to nearby water sources. This is especially true if the city has outdated or in-need-of-repair sanitation & waste management facilities/practices; all bets are off even for cities with topnotch facilities during water-compromising natural or man-made disasters (i.e., hurricanes, tornadoes, earthquakes, wars, acts of terrorism, etc.).
Pollution has been going on so extensively in the past 75 years, in fact, that very few (if any) bodies of water in the US have not been seriously polluted. Just consider all those companies that were dumping toxic waste during the decades when the US was a manufacturing super giant. Then the great race to find radioactive materials like uranium came along.
Mining operations involving these substances have always been very messy--in fact, wherever these mining operations have thrived (over millions of acres), great amounts of radioactive waste have been created and left behind--sometimes involving the fresh water aquifers that would have otherwise provided safe drinking water for hundreds of years to come.
Without doubt, radioactive pollution (made possible and shamelessly sponsored by the mining industry, nuclear power plants and the huge military industrial complex) has not only been mostly overlooked (by the EPA, etc.), it has occurred ad infinitum, without regard to public health repercussions, and, mostly, with impunity. This extensive pollution should be enough to compel all of us to be wary of the water we use every day.
If radiation contamination is an issue for the water where you live, you are in trouble. While there are ways to purify such water sources, it's neither easy nor inexpensive. Also, unless you own a Geiger counter, you won't even be able to tell if your water is radioactive--unless, of course, the government tells you so.
In spite of all this, your best bet is to both filter and purify your water as well as you can. By all means, evaluate what water purification/filtering devices and processes you can afford to get for your home. While you may not be able to get rid of all contaminants, it will still behoove you to reduce the presence of as many of them as you can.
Above all, find out what contaminants have been identified in your area. Then look for means by which you can reduce or eliminate such. Don't put this off. Your health status may depend on what you do, when, and how well.