When iron is present in a water supply, it is quite evident because iron bearing water readily stains plumbing fixtures and cooking utensils. Laundry done in iron water soon becomes stained a reddish brown color. Iron will often times impart a metallic or medicinal taste to the water.
Depending on the concentration of iron in the water, beverages made with this water often have an unappetizing inky black appearance. The flavor of coffee, tea or mixed drinks can be ruined.
When iron precipitates it discolors the water yellow, brown or red. It also accumulates in pipes and valves frequently reducing the flow rate capacity. Iron will cause problems with all water using appliances and reduce the capacity of ion exchange water softeners.
All of the above problems are associated with water when iron is present even in very small amounts. The EPA has established National Primary Drinking Water Regulations that set mandatory water quality standards for drinking water contaminants. The MCL, maximum contaminant level, for iron in drinking water is 0.3 mg/L or ppm of iron. There are some areas of the country that have iron in excess of 70 ppm, but this is extremely rare, and usually we find less than 10 ppm.
A concentration of 0.3 ppm is considered to be the minimum staining level. Above this amount staining will occur.
Iron is dissolved by ground waters containing carbon dioxide. Carbon dioxide will lower the pH of groundwater making it acidic. Generally, the lower the water’s pH, the higher the iron content because the iron compounds in soils and rocks are dissolved by the acid water.
The lower the water’s pH, the higher the iron content is because the iron compounds in soils and rocks are dissolved by the acid water.
Iron exists in three basic forms; ferrous, ferric and bacterial.
Ferrous iron, commonly referred to as “clear water” iron, or dissolved iron, is usually found in water drawn from wells. Ferrous iron, is iron in solution and remains in the ferrous state as long as the water remains underground where oxygen is scarce. Ferrous iron, when brought to the surface, is typically colorless but may have a distinct iron taste.
When water containing ferrous iron is exposed to air oxidation takes place and ferric iron is formed. Ferric iron is insoluble. This insoluble iron is red-orange colored, thus ferric iron is often called “red water” iron. It is not uncommon for this precipitant to settle to the bottom of anything the water is stored in such as pressure tanks, water heaters and water closets.
Iron is rarely found in surface water such as lakes, streams or ponds since iron oxidizes upon exposure to air and settles out.
Iron bacteria are a natural part of the environment in many US States and most other parts of the world. These microorganisms combine dissolved iron or manganese with oxygen. In the process, the bacteria can produce a brown slime that can build up on well screens, pipes and plumbing lines as well as creating objectionable odors.
Iron reduction is tricky because iron is found in three different forms which respond differently to the reduction techniques available in the past. Also water temperature, pH, and other contaminants can influence the success of various iron reduction methods.
Manganese is the elusive element.
Manganese must not be confused with magnesium, one of the constituents of hardness. Manganese is usually found in water that contains iron. Although manganese is more rare than iron, it is even more annoying than iron because it produces extremely objectionable brown or black stains.
These stains occur when the manganese content is above 0.05 ppm, the maximum level recommended by US Public Health Service standards.
Manganese is more difficult to reduce from water than iron. The oxidation rate of manganese is slower than iron and the pH must be considerably higher. The pH must be 8.2 or above for the oxidation to occur. This pH requirement is of particular importance because manganese is most often found in acidic water supplies.
Like iron, manganese is commonly found in deep well waters. When first drawn, the water is clear but exposure to the air converts the clear soluble manganese into a black or dark brown insoluble form. Once this occurs like iron, manganese will stain.