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Iron and manganese are the 4th and 13th most common metallic elements found in the Earth’s crust, respectively. Their presence in a water source does not threaten human health, but can create problems with odor, taste, appearance, and use.
Water percolating through soil and rock can dissolve iron and manganese from certain minerals. Corrosion can dissolve iron from pipes and plumbing fixtures
Theses two metals can remain in solution, depending on other water properties, like pH, oxygen level, salinity, and the presence or absence of other chemicals.
“Reduced” forms of iron and manganese are often found as clear and colorless forms in ground water aquifers, where oxygen content is low. When this water is exposed to air, these elements are oxidized (combine with oxygen) to less water-soluble forms.
Colored forms of iron and manganese become visible in water as they form oxide minerals. Dissolved iron forms white, then yellow and finally red-brown solid particles. Iron oxide particles may or may not settle out and can give the water a red tint. Oxidized manganese usually gives the water a black tint.
Iron and manganese in drinking water are not considered health hazards. In addition, iron-related and manganese-related bacteria are not known to present a health risk. Iron and manganese are both classified by the US-EPA under the Secondary Maximum Contaminant Level (SMCL) standards, which are based on aesthetic factors such as color and staining properties of water rather than health effects.
The abrupt chemical changes affecting solubility are responsible for the staining properties of waters with high concentrations of iron or manganese. Iron will cause reddish-brown stains in laundry, porcelain, dishes, utensils and even glassware. Manganese causes brownish-black stains.
Soaps and detergents do not remove these stains. Chlorine bleach actually intensifies the stains. In rare occasions, adding laundry bleach to manganese-rich water may turn the water purple due to formation of permanganate ions.
Deposits of iron and manganese can build up in pipelines, pressure tanks, water heaters and water softeners. This reduces the available quantity and pressure of the water supply.
Iron and manganese can affect the flavor and color of food and water. They may react with tannins in coffee, tea and some alcoholic beverages to produce a black sludge, which affects both taste and appearance.
Bacterial infestation is a problem that frequently results from excess iron or manganese in water. These non-pathogenic (non-health threatening) bacteria feed on dissolved iron and manganese. For example, iron-related bacteria get their metabolic energy by converting soluble (ferrous) iron to insoluble (ferric) iron.
They form either a red-brown (iron) or a black-brown (manganese) slime and often produce a “foul” odor. These slimes are frequently detected in toilet tanks.
Iron precipitation (or "crystallization") and/or formation of reddish slime inside pipelines and fixtures may cause plugging, staining, metal pitting, and other problems.
Secondary standards are guidelines for drinking water suppliers and are not enforced. The drinking water SMCL is 0.3 milligrams per liter for iron (0.30 mg/l Fe) and 0.05 milligrams per liter for manganese (0.05 mg/l Mn). Tables 1 and 2 give relative rankings for drinking water iron and manganese concentrations, respectively.
A “rotten” smell may indicate the presence of reduced forms of sulfur (such as hydrogen sulfide, a toxic gas) and should be treated with extreme caution.
The relative populations of iron-related bacteria can affect management and treatment choices. Population numbers are expressed as the number of “colony forming units per milliliter (CFU/ml)”. Biological Activity Reaction Test (BART) biodetectors are used to identify the relative presence and populations of iron-related bacteria. See Table 3 and rankings.
Secondary iron and manganese standards are established as guides to manage taste, odor, and color of water. The actual concentrations help identify the best management alternatives.
An alternative drinking water source may be an option if excessive iron or manganese is present in the water supply. An alternate water supply might require drilling a new well in a different location or at a different depth in the same or different aquifer.
Purchasing bottled water is an option when the primary concern is water for food preparation and drinking.
Several methods of removing iron and manganese from water are available. The most appropriate method depends on many factors, including the concentration and form of iron/manganese, whether iron or manganese bacteria are present, and the volume(s) of water that need treatment. Consulting a water treatment professional is prudent because treatment can be complicated
If hydrogen sulfide gas is present, it may indicate that pretreatment is required to fully oxidize sulfur species to sulfates and to control pipe corrosion.
Point-of-use (POU) devices such as reverse osmosis and distillation can remove dissolved iron and manganese. However, these treatment systems are not generally recommended.
Point-of-entry (POE) treatment devices may be needed to remove iron/manganese from all water entering the home. This is because excess iron and manganese are aesthetic problems that affect all potential uses of the water.
The four most commonly applied methods for treating water containing dissolved iron and manganese, are:
Shock chlorination is the most common approach to control iron and manganese bacteria. It is almost impossible to kill all the iron and manganese bacteria in a system. The bacteria population may grow back eventually and repeated shock chlorination will likely be required to maintain water quality.
Repeated shock chlorination becomes time consuming with rapid bacteria regrowth. Continuous chlorination may be more effective. Filters may be needed to remove oxidized iron if continuous chlorination is used to control iron bacteria. Chlorine changes dissolved iron into oxidized iron that will precipitate and drop out of solution.
¶ Table 1. Relative Ranking of Iron Concentrations in Drinking Water |
|
| Iron, as Fe mg/L | Relative ranking |
| < 0.06 | Low |
| 0.06 - 0.12 | Moderate |
| 0.12 - 0.30 | High |
| 0.3 | SMCL |
| 0.30 - 0.90 | Very High |
| 0.90 - 1.80 | Extremely high |
| > 1 .80 | Excessively high |
This water has a very low level or nearly undetectable level of iron, so is not expected to affect use for drinking or household purposes.
Iron itself does not pose a health risk. The iron concentration found in this water supply is not expected to affect use for drinking or household purposes.
Iron itself does not pose a health risk, but some individuals may note a taste or odor. The concentration of iron found in this water supply is not expected to affect use for general household purposes.
This water supply is considered safe to use for drinking, but it may have a disagreeable taste or odor. It may also cause staining or reddish-to-brownish deposits in plumbing fixtures. These problems may result from the presence of iron-related bacteria in the water system, which are not harmful to health. Chlorination and/or additional water treatment may be needed.
This water supply is considered safe to use for drinking. It may have a disagreeable taste or odor, may cause staining, and/or cause reddish-to-brownish deposits in plumbing fixtures. iron-related bacteria may be present in the water system. These bacteria do not pose a health risk, but may seriously aggravate iron problems. Chlorination and/or additional water treatment may be needed.
The iron concentration in this sample does not pose a risk to human health, but is likely responsible for taste, odor, staining, and fouling problems. Specialized water treatment methods, including chlorination, may be needed to use this water for household purposes. Iron-related bacteria may be present in the water system, which are not a health hazard, but will aggravate iron problems.
¶ Table 2. Relative Ranking of Manganese Concentrations in Drinking Water |
|
| Manganese, as Mn mg/L | Relative ranking |
| < 0.005 | Low |
| 0.005 - 0.010 | Moderate |
| 0.01 - 0.05 | High |
| 0.05 | SMCL |
| 0.05 - 0.10 | Very High |
| 0.10 - 0.50 | Extremely high |
| > 0.50 | Excessively high |
This water has a very low level or nearly undetectable level of manganese, so is not expected to affect use for drinking or household purposes.
The manganese level in this water should not affect any uses for drinking or household purposes.
Manganese is not a health concern, but some individuals may find the water to look, taste, or smell unusual. The manganese level in this water is not expected to affect any uses for drinking or household purposes.
This water supply is considered safe for human consumption, but the manganese concentration may cause disagreeable taste or odor, staining, and grayish to blackish deposits. Water treatment, which may include chlorination, may be useful to correct manganese problems. Manganese removal is complicated, so consult with a water treatment firm to choose the best treatment method.
Manganese levels are expected to cause staining, and grayish to blackish deposits on plumbing fixtures, sinks, toilet tanks, appliances, etc. This water supply is considered safe for human consumption, but is likely to have a disagreeable taste or odor. Water treatment, which may include chlorination, will be needed to correct manganese problems. Manganese removal from water is complicated, so consult with a water treatment firm to choose the best treatment method.
Manganese levels are expected to cause staining, and grayish to blackish deposits on plumbing fixtures, sinks, toilet tanks, appliances, etc. This water supply is considered safe for human consumption, but is likely to have a disagreeable taste or odor. Use as a drinking water supply by young children and pregnant women is not advised. Water treatment, which may include chlorination, will be needed to correct manganese problems. Manganese removal from water is complicated, so consult with a water treatment firm to choose the best treatment method.
¶ Table 3. BART Iron-Related Bacteria Test: Results and Interpretations |
||
| Potential aggressivity* | Population, as CFU/ml | Population ranking |
| Absent | Less than 1 | Absent |
| Non-aggressive | 1 to 8 | Trace |
| Moderately low | 8 to 500 | Moderate/Trace |
| Moderate | 500 to 5,000 | Moderate |
| Aggressive | 5,000 to 140,000 | Significant |
| Highly aggressive | Greater than 140,000 | Excessive |
| *The "aggressive" rating suggests that treatment should be started in the near future before conditions degenerate further. | ||