Kathleen
Parrott, Extension Specialist, Housing
Blake Ross, Extension Specialist, Agricultural Engineering
Janice Woodard, retired Extension Specialist,Home Management
and Equipment
| Introduction |
| Activated Carbon and Mechanical Filters |
| Water Softeners |
| Iron Removal Equipment |
| Neutralizers |
| Distillation Units |
| Reverse Osmosis |
| Household Water Treatment Systems |
| Definition of Terms |
Foul taste, smell, or color of your household water may prompt you to investigate water treatment equipment. The publicity about water pollution problems may make you question the safety of your water supply. Or mineral scale buildup may cause you to invest in early replacement of plumbing fixtures and water-using appliances.
Before you attempt a quick and possibly costly remedy, take a first important step. Have your water analyzed. A water analysis will help identify bacteria, minerals, or other pollutants that are present. Interpretation of the test results will help you determine whether the water needs to be treated and, if so, the type of treatment needed. The intended use of the water (whether for drinking, laundry, or all household uses) will also help determine the extent of treatment required.
Keep in mind that no single water treatment device treats all problems, and that all devices have limitations. See table for common water quality problems and suggested corrective procedures.
Do not assume that installation of water treatment equipment similar to that of your neighbors will be the answer to improving your household water quality. Different water supply sources, amounts and types of household uses, and many other variables affect the selection of the proper water treatment system.
See Quick Reference to Common Water Treatment Devices
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General Description Carbon filter devices are available in several sizes and designs. Small units fit on kitchen taps and treat only 100 to 300 gallons effectively before a filter change is necessary. Large under-sink units, often called in-line filters, are designed to treat up to 1500 gallons. On such a unit the canister is connected to the cold water line. Other styles are available that treat all household water. An extra filter cartridge or canister is often included with the initial purchase. Check on availability of filters and cost of replacement filters at time of purchase; they may be available from the same dealer, at plumbing supply stores, or by mail order.
Design greatly influences efficiency. Variations include use of powdered carbon or blocks of carbon instead of granular carbon. Those filters containing more carbon will usually treat more water before replacement is necessary.
Mechanical filters are frequently combined with activated carbon filters. Small mechanical filters, using spun cellulose, attach to a tap or can be installed under a sink. Filters to treat all the water supplied to the house may use sand or gravel.
Limitations Activated carbon filters do not remove nitrate, bacteria, or metals. Concern about the growth of harmful bacteria in these filters has been raised in the past. However, recent research by the U.S. Environmental Protection Agency indicates that the types of bacteria found in water samples obtained from this type of filter create no health hazard if the filter is properly maintained. As a precaution, however, activated carbon filters are recommended for use only on microbiologically safe water.
Maintenance Setting up a regular maintenance schedule for filter replacement is necessary, because there is no easy method for detecting that a filter is no longer working effectively. The frequency of filter cleaning or replacement depends largely on the level of pollutants in the water supply and the quantity of water flowing through the filter.
A mechanical filter may become clogged if not cleaned or replaced periodically, resulting in loss of water pressure and a reduction in flow. Filters using sand or gravel require automatic or manual backwashing to remove trapped particles.
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General Description The most common way to soften household water is to use a cation exchange water softener. A synthetic resin with a strong attraction for calcium, magnesium, and other positively charged metal ions (cations) is first saturated with sodium cations from a salt (sodium chloride) solution. As the water passes through the resin, the sodium exchanges with calcium and magnesium.
Softeners are automatic, semi-automatic, or manual depending on the system for regeneration of the resin. Each type is available in several sizes and is rated on the amount of hardness it can remove before regeneration is necessary.
Limitations Individuals on a sodium-restricted diet should consult a physician before using softened water. A possible solution is to have drinking and cooking water lines bypass the water softener. Water softening units also remove small amounts of iron. However, using a softener to remove iron in naturally soft water is not advised. Refer to the iron filter section of this publication.
Maintenance When the resin is filled to capacity with calcium and magnesium, it must be recharged. Fully automatic softeners regenerate on a preset schedule and return to service automatically. Regeneration is usually started by a time clock, although some units start regeneration by water-use meters or hardness detectors.
Semi-automatic softeners have automatic controls for everything except for the start of regeneration. Manual units require manual operation of one or more valves to control backwashing, brining, and rinsing.
In many areas, there are companies that provide a water softening service. For a monthly fee,the company installs a softener unit and replaces it periodically with a freshly charged unit. The replacement schedule depends on the water hardness and the amount of water used.
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Water with a high iron or manganese content is not considered a health problem, but can be very objectionable in taste, odor, or appearance if iron is present in amounts greater than 0.3 milligrams per liter or manganese is present in amounts greater than 0.05 milligrams per liter.
Iron bacteria are nuisance organisms often associated with soluble iron in water. Because they cause a slime buildup, they can be quite objectionable with iron concentrations as low as 0.1 milligrams per liter ferrous (soluble) iron.
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 disinfection) are required to control iron bacteria. Shock chlorination must include the well and pumping system.
General Description and Maintenance Five types of iron-removal equipment are available:
The filter bed must be backwashed frequently to remove the accumulation of iron particles. For backwashing, a flow rate more than double the normal service flow rate is usually required. The exhausted manganese must be recharged by adding potassium permanganate.
Acid water below a pH of 6.8 will pick up manganese from the green sand and cause loss of oxygen exchange capacity. Therefore, neutralization treatment may be necessary. Also, the slime produced by iron bacteria will clog the filter.
Polyphosphate is only effective in cold water. Heating the water will release the iron so that oxidized iron accumulates in the waterheater. The heated water will be rusty and unsatisfactory for home use.
This method also destroys iron bacteria. When the bacteria cannot be permanently eliminated by shock chlorination, continuous chlorination is required.
Limitations Iron removal from your water supply can involve complex choices. Careful planning is needed when iron removal equipment is used in conjunction with other water treatment equipment. The type of iron removal equipment chosen depends on the type and quantity of iron in the water, the characteristics of the water supply, other water treatment equipment in use, and the user's requirements for cost, ease of use, and maintenance.
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General Description 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.
Limitations and Maintenance Neutralizers using soda or sodium compounds increase the sodium content of water which may be a health concern. Using calcite to neutralize water increases calcium, which increases water hardness. These factors must be considered in your treatment choice. All systems require routine maintenance to replenish the chemical used to neutralize the water.
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General Description Distillation units boil water to create steam which is then condensed and collected as purified water. Most impurities remain in the heating chamber and must be periodically removed. Units vary from the kitchen countertop size to larger units.
Limitations Removal of minerals produces water that can have a bland taste. Because a kitchen location close to point of use is preferred for smaller units, counter or cabinet space must often be given up. Also, distillers are expensive to operate.
Some distillers allow contaminants with a boiling point lower than water (e.g. some pesticides and volatile solvents) to vaporize with the water and recondense with the treated water, which means they remain in the treated water. Others have a volatile gas vent that releases these products to the atmosphere.
Maintenance Design of the unit is important because minerals and other contaminants accumulate in the boiling chamber and can interfere with the operation of the unit. Hard water can cause scaling in a distiller. Some units are easily cleaned by hand while others require washing with a strong acid.
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General Description Contaminants are removed by forcing water through a membrane having microscopic holes that allow water molecules, but not larger compounds, to pass through. Water flushes away the contaminants held by the membrane.
Membranes are made of a variety of materials that differ in effectiveness for different chemicals. Be sure to study water test data and identify the chemicals to be removed.
Limitations and Maintenance Although reverse osmosis removes many organic chemicals, it does not remove all. For instance, it will not remove chloroform. And it does not remove 100 percent of most chemicals.
These units waste large amounts of water. Most units will discharge up to 50% or more of total water as waste.
The membrane can develop problems from precipitate buildup and scaling. A softener must be installed ahead of the reverse osmosis unit if hard water is used. Otherwise, the minerals will quickly plug the membrane filter.
Frequently, mechanical and/or activated carbon filters are installed before the reverse osmosis unit to remove turbidity and improve taste and odor. This can result in improved overall water quality and extend the life of the reverse osmosis membrane.
The reverse osmosis membrane will need periodic replacement according to the manufacturer's recommended schedule. Occasional cleaning and flushing of the whole reverse osmosis unit may be required.
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Chlorination does not remove nitrate or other chemicals, but may oxidize organics and some minerals such as iron Chlorine metering pumps must be calibrated and maintained carefully Using a carbon filter after chlorination will remove any excess chlorine and chlorine based chemicals that may form
Other Methods Other methods of disinfecting water include boiling distilling pasteurizing treating with ultra-violet light, and treating with ozone Chlorination distillation or boiling for 15 minutes are the usual methods used to purify water for household use. Disinfection by ozonation or ultraviolet light methods are replacing chlorination in some water treatment plants, and are becoming more popular for home uses
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.
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ACIDITY - A condition of water when the pH is below 7. See pH.
ALKALINITY - A condition of water when the pH is above 7. See pH.
BACKWASHING - The process of reversing the flow of water to restore or clean a filter.
FLOW RATE - The quantity of water available or needed commonly measured in gallons per minute, per hour, or per day.
GRAINS PER GALLON - The weight of a substance, in grains, in a gallon. Commonly, grains of minerals per gallon of water is a measure of water hardness. 1 grain per gallon = 17.1 milligrams per liter.
HARDNESS MINERALS - Minerals dissolved in water that increase the scaling properties and decrease cleansing action usually calcium and magnesium.
ION EXCHANGE - Process whereby one mineral is substituted for another.
NEUTRALITY - A condition of water when the pH is at 7. (neither acid or alkaline) See pH.
OXIDATION - Causes the impurities to precipitate, and this reduces water impurities, such as iron, manganese, hydrogen sulfide, and many organics.
PEAK USE RATE - The flow rate necessary to meet the expected maximum water demand in the system.
pH - A measure of the acidity or alkalinity of water. Below 7 is acid, above 7 is alkaline.
REGENERATION - Process which restores the ion-exchange material (zeolite or resin beads) to useable condition.
SHOCK CHLORINATION - Using high dosages of chlorine (200 to 500 milligrams per liter)
SOFTENING - The process of removing hardness caused by calcium and magnesium minerals.
Publication #: 356-481
Adapted from a publication by Annette Bach and Darnell Lundstrom, North Dakota State University Extension Service by: Kathleen Parrott, Blake Ross, and Janice Woodard.
Disclaimer and Reproduction Information: Information in NASD does not represent NIOSH policy. Information included in NASD appears by permission of the author and/or copyright holder. More
