Water is life. That is a fact that cannot be stressed enough. It is not only vital for the maintenance of life itself, but it is also vital for keeping ecosystems and civilizations afloat. However, due to various reasons most commonly caused by man, water can get contaminated. Sometimes, water contamination can go to the point that it is rendered unsuitable for human consumption.
There are different forms of water contaminants and each of them has their own way of making an impact on your water quality.
Pathogens - illness causing bacteria and viruses
These are microorganisms found in water that cause disease and sometimes death to various creatures living in water. While microbes typically live in water without consequence, some of them are actually pathogenic. Worse, they tend to multiply quickly to dangerous levels.
Coliform bacteria are the most common pathogens found in water. Other famous pathogens that are considered as water contaminants include Giardia, Salmonella, Cryptosporidium, and Novovirus.
If you get your water from a public supplier, you probably don't have to worry so much. They add chlorine and monitor bacteria. And if you don't like the taste of chlorine, pitcher or faucet mount water filters can remove it.
Organic chemicals are often residues due to various human activities. The seepage of organic waste from excreta largely contributes to water pollution due to organic waste. Modern day animal farms use a lot of chemicals to maximize their profit.
Other organic contaminants include detergents, oil, pesticides/herbicides, disinfection byproducts (ex. chloroform), chlorinated solvents, and VOCs (volatile organic compounds).
Unfortunately not all of them are regulated by the Environmental Protection Agency (EPA). That means your water supplier does not need to test for them. And as a consequence also does not need to take measurements to eliminate them from your water.
According to EPA, Granular Activated Carbon (GAC) filters are an effective way to remove organic chemicals from water. GAC filters are part of most reverse osmosis systems.
Inorganic chemicals are also dumped into waters all over the world. One common inorganic pollutant is ammonia, a byproduct of a number of chemical reactions and an ingredient to some compounds extensively used by man.
Nitrates and phosphates are also common inorganic pollutants. Heavy metals, even in small amounts, are incredibly toxic.
Lastly, certain ions and halides are known to dramatically change water’s pH levels, making it either too acidic or too basic.
Reverse osmosis, distillation and activated alumina filters are the most common filtration methods to treat these water problems.
Micro plastics, the newly discovered threat
2017 "The Guardian" published an article about plastic fibers, found in tap water all over the world. It sums up the finding from Orb Media stating that tiny micro plastic fibers are everywhere, in our water, our food, our air.
The health impact is not completely clear yet, but that plastic is not a healthy part of our daily diet makes a lot of sense to me.
As far as I know, there are no recommended filter techniques for micro plastic.
I assume, if you use a very fine filter with holes smaller then the plastic particles in your water, you would be fine. Some gravity filter cartridges and reverse osmosis membranes have the extremely small holes.