| Treatment process |
What it does |
Contaminants Removed/Altered |
| Filtration
|
By passing water through a cartridge, granular media or other device, contaminants are subtracted from the water to make it cleaner. In some cases this is a "straining" effect; in other cases the contaminants are removed by adsorption- the contaminants have an attraction to the surface of the filter.
Often, minerals such as iron and manganese are oxidized prior to filtration in order to create large enough particles to filter. In addition, pH changes may be needed.
|
Iron, manganese, arsenic, silt, sand, organics, some heavy metals, radon, cysts |
| Ion exchange (softening, etc)
|
As water runs through a resin in a vessel, charged electrical particles (ions) are exchanged for other ions which are more desirable. Often this process can be reversed by regeneration of the resin
|
Hardness (calcium, magnesium), iron, manganese are commonly removed. Other ions such as arsenic and nitrates can be removed this way.See how a softener works.
|
| Oxidation
|
By introducing oxidizer such as chlorine, ozone, oxygen, or ozone (there are others too), ions' electrical charges change (get more positive). This is often done to prepare for filtration. Sometimes oxidation alone is sufficient to manage hydrogen sulfide (a gas which has a rotten egg smell).
|
Does not technically remove anything; alters water chemistry. |
| pH correction |
By dissolving an alkaline (basic) material into water, low pH (<6.5 units) can be adjusted to prevent corrosion. Often accomplished with a calcite filter/contactor which uses clean lime to correct pH.
Sometimes high pH's are controlled by acid injection. This may be done for scale control.
|
Usually does not technically remove anything; alters water chemistry-except via air stripping (see below). Controlling low pH often reduces levels of leached copper and lead in plumbing systems.
|
| Aeration (air stripping)
|
By forcing high volumes of air through water dissolved gasses and other volatile compounds are liberated and vented away. (If you aerated carbonated soda, it would become very flat)
|
Radon, volatile organics, can raise pH, hydrogen sulfide
|
| Disinfection
|
Adding a disinfectant (chlorine, ozone, ultraviolet light) kills or disables microbes to make water safer to drink. |
Kills microbes, or in the case of ultraviolet, prevents multiplication
|
| Reverse osmosis (and other membranes)
|
Water is passed by a very fine filter (membrane) under pressure. While water is squeezed through, many contaminants are flushed to waste. Often used as a drinking water solution. Typically silt, manganese, iron and hardness are removed prior to reaching the membrane in order to prevent fouling.
|
Ions: sodium, chloride, lead, nitrates, arsenic, etc. |
| Distillation
|
By boiling water, vapor is formed and condensed. The contaminants are left in the boiling chamber.
|
Distillation removes nearly all contaminants from water but is rather energy-intensive.
|
| Sequestration
|
By surrounding ions with a polymer, they are shielded from posing problems. Often accomplished by injecting a solution into the water. Can also help with corrosion control |
Can be used to control mineral staining and corrosion
|
| Magnetic devices
|
Supposedly alter the structure of water. Some claim that they help with scale control. We have seen no evidence to support these claims. |
?
This page reflects our feelings on this and similar matters.
|
