Our drinking water comes mostly from rivers or lakes. Municipal water treatment plants filter out sediment, excess minerals, etc. They also disinfect the water to destroy pathogens.
The output must meet strict standards determined by federal law. It is safe to drink, but many consumers do not find it satisfactory.
In part, dissatisfaction comes from watching ads for bottled water, which underscore the purity of a store-bought product. Consumers need to remember that their municipal drinking water is held to strict standards, and that bottled water is no cleaner or healthier.
Not only that, but the plastic bottles themselves constitute a major environmental menace. Still, people may have good reason to want to further purify their tap water.
Why people want to filter drinking water
Municipalities use chlorine to disinfect the water. Many also add fluorine to promote good dental health in children. If chorine kills bacteria, it stands to reason that it’s not especially good for us.
One reason to filter tap water, then, is to remove these additives, as well as additional minerals that come from water mains and pipes after the water leaves the treatment plant.
Tap water in some places doesn’t taste very good. Or perhaps it doesn’t smell very good. It meets government standards for safety, but not the standards and preferences of some consumers.
Unfortunately, some companies use scare tactics either to foment suspicion about government standards or water safety in general. Beware of anyone using fear and distrust to persuade you to buy products from them!
In still other places with naturally hard water, lime scale or sediment can affect the taste and appearance of tea or coffee, not to mention foods cooked using the water. It can also make it difficult to keep pots, teakettles, etc. clean and may even shorten their lives.
Available filtering methods
Some refrigerators deliver filtered drinking water through the door. If you own a refrigerator like that, you need to replace the filter inside the refrigerator from time to time. (And of course, it has to go in the trash.)
You can also easily find water-filtering pitchers that have comparable disposable filters. Some people who are especially susceptible to the fear mongering filter the filtered water from the refrigerator with these filtering pitchers!
It is also possible to filter the tap water by installing some kind of filtration system to the kitchen plumbing. Various technologies exist, the most common being reverse osmosis.
What’s osmosis? I was afraid someone would ask.
Technically speaking, it’s the passage of a solvent (water, for example) through a semipermeable membrane that blocks the passage of whatever is dissolved in it (called the solate).
Nature prefers equilibrium. If tap water and salty water are separated by a semipermeable membrane like Gore-tex, the relatively pure water will flow through the membrane to dilute the salty water.
Instead of creating an equilibrium, reverse osmosis achieves a removal of the salt (or other solate). Therefore, reverse osmosis forces nature to do something it wouldn’t ordinarily do.
It’s sort of like the concept of torture—apply enough pressure to force the victim to act contrary to his or her true intentions.. Pressure applied to the side with the highest concentration of solate will force the solvent to the other side of the membrane.
Since reverse osmosis deliberately works contrary to natural tendencies, it’s not surprising that it has only recently become practical. Researchers managed to use it to remove salt from water in the 1950s, but the amount of fresh water they created was too small for the technique to be practical.
After more research, more advanced filters were developed. In 1965, reverse osmosis had advanced enough that a desalination plant began operation in Coalinga, California. Perth, Australia, a very dry city surrounded by the ocean, gets 17% of its drinking water from desalinated seawater.
On a smaller scale, it is now possible to install reverse osmosis water filtration at home.
It comes in two styles. An under-the-counter system forces water through at least three and as many as five filters and into a storage tank.
You can use the regular faucet for washing dishes and get filtered drinking water from the storage tank through a separate faucet.
Or, you can get a counter-top reverse osmosis system. Hook up a feed line to your regular faucet and draw purified water from the unit into a pitcher. This kind of reverse osmosis is slow, and the filter needs to be replaced regularly. That’s the trade-off for something comparatively easy to install that does not require a major plumbing project or permission from the landlord.
In either kind of reverse osmosis system, the filtered output is much less than the unfiltered input. The rest, which contains all of the leftover minerals, becomes wastewater.
Source: How Reverse Osmosis Works / How Stuff Works