Iron in the ferric form and manganese stains clothes and plumbing fixtures. Ferrous iron is in the dissolved form and cannot be seen in water. When water containing ferrous iron is exposed to air, the iron oxidizes and rusts. Ferric iron, rusted iron, usually appears as brownish red colored particles floating in the water.
Water with a high iron or manganese content is not considered a health problem, but it can be very objectionable in taste, odor or appearance. Iron bacteria are nuisance organisms often associated with soluble iron in water. Because they cause a slime buildup they are objectionable. Calcium is an essential nutrient for this bacteria. The presence of iron bacteria is indicated by a gelatinous slime on the inside wall of the toilet flush tank and gelatinous "rusty slugs" being discharged at the tap. High dosages (200 to 500 milligrams per liter) of chlorine (known as shock chlorination or disinfecting) are required to control iron bacteria. Shock chlorination must include the well and system.
Four types of iron-removal equipment are available:
Iron Filters. Iron filters are only useful for removal of ferrous iron and manganese; ferric iron will plug them. They appear similar to water softeners but contain a bed of natural or synthetic manganese green sand. Manganese dioxide oxidizes iron and manganese and the oxidized particles are then filtered out in the lower part of the bed.
Water softeners. All water softeners will remove iron; the rating for iron depends on whether the regeneration will remove the iron from the zeolite or not. Water softeners contain a zeolite mineral that will remove soluble iron on an ion-exchange basis (the same way calcium and magnesium are removed in water softening). The slime produced by iron bacteria will clog the zeolite and reduce its effectiveness.
Polyphosphate Feeders. These units contain a phosphate compound which coats the soluble iron and prevents its oxidation when the water is exposed to air. The compound is not effective against iron that has already oxidized. When some waters are heated, the raised temperature will reduce the effectiveness of the polyphosphate so that oxidized iron will accumulate in the water heater. (Polyphosphate is only effective in cold water. Heating the water will release the iron.) The heated water will be rusty and unsatisfactory for home uses.
Chlorination and Filter. Chlorination followed by filtration through a sand filter can remove any quantity of iron in any form. The chlorine oxidizes and precipitates the iron and the filter strains out the particles. Carbon filtration may be required to remove excess chlorine residue. This method also destroys iron bacteria. When the bacteria cannot be permanently eliminated by shock chlorination, continuous chlorination is required.
Neutralizers. This system treats corrosive (acidic) water. Alkalinity and pH are increased through processing. Passing the water through granular calcite (marble, calcium carbonate or lime) is the most common method of home treatment. A mix of calcite and magnesium oxide also is used. if the water is very acidic or if a high flow rate is needed, a system to chemically feed soda ash, sodium carbonate or caustic soda (sodium hydroxide) may be necessary. These systems increase the sodium content of water, whereas using calcite or lime increases calcium.
Chlorination. Both municipal systems and households can disinfect water by adding chlorine. Household systems commonly use household bleach. Chlorination does not remove nitrates or other chemicals, but may oxidize organics and some minerals such as iron. Chemical metering devices must be maintained carefully. Using a carbon filter after chlorination will remove any excess chlorine and chlorinated chemicals that form.
Other methods of disinfecting water include boiling, pasteurizing, treating with ultraviolet light, and treating with ozone. These methods are usually less practical than chlorination or not readily available. Note that sterilization (boiling water vigorously for at least two minutes) kills all organisms. Disinfecting reduces the concentration of organisms to safe levels. Devices to kill or remove bacteria or viruses are termed purifiers. Chlorination, distillation, or boiling for 15 minutes are the usual methods used to purify water for household use.
Disinfecting by ozonization or ultraviolet light methods are replacing chlorine in some water treatment plants, but are not yet readily available for home use. Some filtration units with silver-coated activated charcoal blocks are being sold for removal or killing of bacteria. Before purchasing such a unit, evaluate it carefully and check for sufficient test data and certification to assure its effectiveness.