Water is referred to as a universal solvent. It naturally dissolves an absorbs substances. Without these dissolved substances life wouldn’t be possible. Another way to put it is, not everything present in water needs/should be removed.
Bacteria: Not all bacteria are pathogens (disease causing). Most treated water contains some bacteria. There is always some bacteria that is shielded from or is resistant to the disinfectant or the disinfectant wasn’t given enough time. Either way, in a normal situation bacteria in your water is not a problem. Unless they are of a specific type. Some examples of pathogenic bacteria are ecoli and fecal coliforms, both of these are indicators of sewage contamination in the water supply. I will mention giradia and cryptosporidium here, they are technically not bacteria. Officially giradia is a cyst and crypto is an oocyst. All that really means is they are infectious during a different stage of their life cycle. Giradia and crypto are still microspic and have evolved resistance to disinfection with chlorine. The best way to remove them is disinfection with ozone, uv and filtration.
Minerals: As water passesc through and over soil it picks up dissolved minerals, commonly calcium, iron and manganese. This is sometimes referred to as hardness. Most people prefer the taste of water with minerals present. Just look at the sales of mineral water. Now the minerals in water re not enough to sustain us completely, but they help us meet our daily quota. Removing hardness is possible with a water softener. Artificially softened water isn’t recommended for anyone to drink, especially people with high blood pressure or heart conditions as the minerals are replaced with sodium. Naturally soft water should have normal levels of sodium. Softened water is much easier on appliances, some warranties are even voided if you don’t use soft water.
Organic Compounds: Present in almost every source of water. In small amounts they pose little risk. Organic compounds should be removed, settled and/or filtered to prevent the formation of disinfection by products (DBP). DBPs like trihalomethane and halo acetic acid are suspected carcinogens. Organic compounds can also take the form of tannins. Tannins are a coloration of the water and are one of the hardest things to remove from water. Think about separating tea from water, easy to remove the leaves, but how do you remove the color? That is the challenge of removing tannins from your water.
Inorganic Compounds: These are your sands, stones, rocks and non nutrient minerals. They pose no useful purpose and are usually easily removed with settling. Really small inorganic compounds can sometimes be colloidal. Meaning each particle has the same electrical charge and they spread out never settling on their own. Some can be filtered, most need some chemical to attract them electro-statically.
Radioactive Compounds: These are exactly what you think. Particles that emit radiation. If there is nuclear fallout (either from a bomb or meltdown) these will be everywhere and will kill you fast. Especially if you drink them. But those are not the only sources. The other sources are much more common. Radioactive particles exist in nature. Usually in very small doses. The largest source of radioactive material outside of power plants is hospitals. Followed by cancer patients receiving chemotherapy. Hospitals dose the patients, and the patients transfer the particles to the sewage system. Radioactive particles stay radioactive inside living organisms and can be transferred from one organism to another, typically by eating and drinking.
Heavy metals: Think of these as you would radio active particles, except these don’t emit radiation. The toxicity from heavy metas comes from volume. The more of them that are in your body the sicker you get. There is also the process of biomagnification, one bacteria eats one heavy metal particle. The next level eats 10 bacteria a day, then 10 more, all the way to the top of the food chain where the contamination can be lethal. Eating one toxic fish can be very bad for us.
Chemical Contamination: Also known as pollution. Get as much as this out of your water as you can. I unfortunately cannot tell you exactly how to do this as each chemical will need a slightly different treatment process. When it comes to this area, specifics matter. I don’t want you to think it will be difficult to remove the chemical, just that what works for one chemical might not work for the next.
Pharmaceuticals: Similar to radioactive particles, pharmaceuticals also make it to the sewage system. They also survive most wastewater treatment processes which tend to be biological in nature. Check out this from Boston regarding how the caffeine found in the harbor roughly matches the caffeine consumed by Bostonians. This is a relatively benign example but the same is true for more harmful drugs.
Hormones and Hormone Mimics: This group is similar to pharmaceuticals and behave similarly in the environment. Hormones are the chemicals that regulate our bodies’ functions. Hormone mimics are chemicals that trick the body into thinking they are natural hormones. Hormone mimics come from the breakdown of plastics. Take a moment and think of all the plastic that has been left out in the environment. There is one more significant fact about hormone mimics, if there is a way to treat for them, it is so new that nobody is doing it yet. This is currently the cutting edge of water treatment research.
I will focus on what chemicals typical treatment processes add to the water in another article. There is a lot of confusion around the treatment chemicals, specifically regarding chlorine. I will remove some of that confusion next.