Basics of water purification
Pure water has become a rather scarce commodity in our day and age. There are very few unpolluted aquifers left, most people have to rely on filtered water.
Let's overview the basic methods of purifying water. And even though the material on this page refers to the laboratory methods, it still gives a good idea about what is involved here.
If you would like to obtain more information on the subject, you can get it from books on clinical or laboratory chemistry.
Water originating from the natural sources contains a variety of inorganic, organic and microbiological contaminants. They cannot be completely removed by any single water purification system, but a combination of several methods can be used to produce water of type I purity or better.
(Types II and III are the lower grades of laboratory water).
Distillation
Distillation of water in glass will remove nonvolatile organics, inorganic impurities and microbiological organisms. Volatile impurities, such as ammonia, carbon dioxide, chlorine and low-boiling organic compounds will be present in the distillate. Distilled water meets the specifications of type II water or type III water.
Deionization
Deionization is accomplished when water is passed through basic and acidic ion-exchange beds or a mixture of the two. The treatment results in the exchange of hydroxyl and hydrogen ions located on the surface of the resin for cation and anion impurities.
The resins eventually lose their exchange capacity but can be regenerated by treatment with acid and alkali.
Ionized impurities are those which are present in ionized form, soluble salts are a good example. Many organic substances, even though fully dissolved, do not break into ions, which means deionization of water has no effect on them.
Water containing less than 1 million colony-forming units per litercan be deionized to produce type II water. Further treatment with activated charcoal and membrane filtration to remove organic impurities, particulate matter, and microorganisms is necessary to produce type I water.
Filtration
Filtration of water through semipermeable membranes with pore sizes of about 0.2 micrometer will remove insoluble matter, emulsified solids, pyrogens and microorganisms.
Sterile water can be produced by filtration through membranes with a pore size of 0.3 micrometers (300 nm) or less.
"Sterile" means it contains no microorganisms. It does not mean there are no contaminants.
Adsorption
Organic impurities can be removed from water by adsorption on activated charcoal, clays, silicates or metal oxides. A combination of deionization, adsorption and filtration will produce type I water.
"Reverse osmosis"
Reverse osmosis is the passage of water under pressure through a semipermeable membrane made of cellulose acetate, aromatic polyamides, cellulose acetobutyrates or other materials.
This treatment removes approximately 90 percent of dissolved solids and 98 percent of organic impurities, insoluble matter and microbiological organisms.
Reverse osmosis removes only about 10 percent of ionic impurities and does not remove dissolved gases.
This method of water purification will produce type III water (the lowest laboratory grade) and is frequently used to treat water before its passage through ion-exchange resins.
Some commercial enterprises offer water filtered using reverse osmosis.
You can decide whether or not it is worth your money.
"Reverse osmosis" does not have anything to do with "osmosis".
The process of osmosis or osmotic pressure does not play any role in this type of filtering.
A probable reason why this term is being used in connection with this type of a filter is because semipermeable membranes can be used to produce a phenomenon of "osmosis".
In order to figure it out we must first understand what osmosis is.
If you take a container and divide it into two parts using a semipermeable membrane and then add some soluble stuff to one half, for example, sugar or salt, then the level of water would raise in that part of a container where soluble compound was added.
There are many types of commercially available semipermeable membranes, they pass water and other fluids, but would not under ordinary pressure allow through noticeable quantities of solutes.
The process that would be taking place is simply equalization of solute concentrations on the different sides of a semipermeable membrane.
This process is called "osmosis" and it can be formally described as if some sort of a pressure pushes water from one part of a container into another.
The pressure which is generated in this process is called "osmotic pressure".
In a similar fashion, if we have communicating vessels and we install a semipermeable membrane in the communicating channel and then add some soluble compound to one vessel, then the water level in it would rise.
To feel the effects of osmotic pressure, you can dissolve a teaspoon of salt in some half a cup of water and draw it into your mouth.
Keep it there for a few moments and then spit it out.
You would feel as if the mucous membrane inside your mouth has become "wrinkled".
This happened because the water from the cells was sucked out by osmotic pressure of a concentrated salt solution.
An opposite effect takes place when tissues are immersed into distilled water.
In this case osmotic pressure works in a different direction, the cells absorb water.
Fragile cells, like those in blood, would rupture pretty fast, if placed in water.
This happens because the solution inside them is 0.9 percent sodium chloride, just like in other body fluids, and it can create enough osmotic pressure to absorb water that would rupture the cell if those end up in a solution of a lower concentration of salt.
The walls of the cells are semipermeable, they may pass a limited amount of water, as well as liquids that dissolve fats, like alcohol, solvents, but they are impermeable to many solutes.
The household "reverse osmosis" filter consists of several layers of semipermeable membrane.
It is quite expensive, over US$100; it requires pressure of at least 40 psi in order to drain the filtrate at an acceptable rate, that would allow to produce a few liters per hour.
That is why this type of a filter can only be connected to a tap in order to function.
The obvious question is - what happens to the contaminants which have been filtered out?
Obviously, if the filter blocks their passage to a certain extent, then they would keep concentrating inside the membrane. And, as more and more contaminants will be permeating the membrane, more would be pushed through the filter wall by the flow of water.
Generally, the performance of any filter depends on the level of "impurities" at the input - be that water, air or sound filter.
The more "impurities" are there at the input, more would be coming out.
An ordinary ear plug would probably be of little help when standing next to a jet engine. Even if it would muffle half of the noise, whatever would go through would simply be too much.
Essentially the same applies to a water filter.
That is why the only way to avoid degradation of a filtering properties with time is to have a replacement filter, which deals with the more "crude" components, those which can be filtered out using the cheaper add-ons.
Some so-called "reverse osmosis" filters have an activated carbon cartridge inside, you replace it several times during the lifetime of the semipermeable membrane.
This is done to protect the membrane from contaminants that can be filtered out by using the less expensive ways.
And, as we have seen, the picture with regard to filtering out ionized impurities is not very encouraging with this type of filter, it can be as low as 10 percent.
One of the substances used for fluoridation of drinking water is sodium fluoride, a very potent protoplasmic poison.
Sodium fluoride is listed as poison in Merck's index.
It is such a potent poison that it is classified as a restricted substance and can only be sold to the licenced commercial enterprises!
Sodium fluoride, just as sodium chloride (kitchen salt) is dissolved into ionized form in water.
This means that as many as ninety percent of it may be passing through that so-called "reverse osmosis" filter.
And since it can only function at high pressure, you cannot run the water through it more than once, as you can do with a table-top carbon filter.
Some companies offer drinking water, which is somehow labelled as "distilled" and also "deionized water".
And even though it might not be spelled out anywhere on a label that this water is for drinking, it is sold in the same bottles, as other types of drinking water.
It is only logical to assume that people would only pay for water, which they cannot get from a tap.
In other words, we expect bottled water to be natural, unpolluted water, coming from a spring, which is located in an upolluted aquifer.
The truth is that some bottled water companies sell plain tap water, which underwent the most rudimentary processing.
Deionization, for example, is a very basic and inexpensive process, it does remove some ionized impurities (soluble salts), but has no effect on impurities that do not get split into ions when they dissolve.
Organic pesticides, solvents have no problem passing through an ion-exchange resin bed.
With regard to distillation, one should be very skeptical about the claims of the producers.
A properly distilled water is rather expensive and there is no way it can be sold for a dollar or two a gallon.
First, it is a very energy-intensive process. Just to imagine how much energy would it take to evaporate a gallon of water!
And if you sell it by the thousand gallons, then it has to be a pretty big boiler.
On top of that, boiling water in distillation tanks would inevitably result in deposition of plenty of hard scale on the walls of those tanks, which would render them useless in a very short period of time.
As a comparison, it takes plenty of resources to make sure that boilers would not be ruined by deposition of scale.
The water has to be treated before it goes into a boiler, plenty of chemicals are added to it to prevent scale formation.
If you ever dipped your fingers into water that is ready to go into the boiler, you know that it feels "soapy".
Essentially the same treatment would have to be performed on water before it can be poured into an evaporation tank, which, obviously, would defeat the purpose of producing pure drinking water.
The real reason why some companies put a label "distilled water" on their bottles of drinking water is probably because so far nobody sued them for misrepresentation.
It is, of course, possible to find distilled water, but not for a dollar or two a gallon.
And if you buy it, then you should know that it is very damaging to tissues.
This is because all body cells contain salts, primarily sodium and potassium chloride.
A normal concentration of those salts is equivalent to 0.9 percent of sodium chloride solution.
If cells are in contact with distilled water, osmotic pressure would be drawing water into them, which can cause their rupture.
There is a list of common water contaminants, which was compiled by EPA. It has a max safe level for each contaminant.
It is available on my site notSmoking.info/poisons.htm
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