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Treatment Devices for Drinking Water

Introduction

Water quality concerns users of public and private water systems.

Some indicators of contaminated water include off-tastes, odors, or visible particles. However, some dangerous contaminants in water are not easily detected. Therefore, accurate water testing is needed to determine the safety and quality of water for home use. Water testing also is important to identify the need for water-conditioning equipment.

Treatment Systems

Water quality involves the degree of acceptability for household uses such as drinking, cooking, bathing, and laundering. Water-conditioning equipment improves quality by reducing turbidity (suspended sediment) and removing calcium, iron, magnesium, and sulfate. Conditioning treatment can produce a clearer, better tasting, and better smelling water and can increase its function for household use. Some treatments also reduce other contaminants (nitrates, arsenic, or lead) that are known or suspected health hazards.

Four common water-treatment systems for household use are distillers, filters, reverse osmosis (RO) units, and softeners. Factors to consider before buying any of these systems include:

  1. Type and amount of water contaminants.
  2. Equipment cost.
  3. Operating and maintenance costs.
  4. Operating and storage space.
  5. Ease of use.

Some equipment improves the water quality for all household uses while others primarily improve safety and quality of drinking water. Before buying water-treatment equipment, have your water supply tested by a recognized certified water-testing lab. Identification of the type and level of contaminants is important in getting the right system.

Distillers

Distillers produce almost pure water. When the distiller is operating, tap water in a boiling tank (often made of stainless steel) is heated to boiling. Steam is produced, rises, and leaves most impurities behind. The steam enters condensing coils, where it is cooled and condensed back to water. The distilled water then goes into a storage container or is piped to a special faucet.

Features that distinguish between distillers include:

  1. Capacity of the boiling tank.
  2. Type and size of the water-storage container.
  3. Rate at which distilled water is produced.
  4. Presence of automatic features.
  5. Location of unit for convenience of use and ease of maintenance.
  6. Wattage rating (650 to 1,500-plus watts).
  7. Batch or continuous process mode of operation.

Storage containers can be glass, metal, or plastic. Each type of container is satisfactory when cared for as the manufacturer directs.

Large distillers can distill about one-half gallon of water per hour. Smaller units produce less than one quart of water per hour. The cost of producing distilled water depends on the appliance and the local electric rate. Although the distiller has no parts to replace, it is not maintenance-free. Scale must be removed from the boiling tank. Frequency of cleaning the distiller varies with the quantity of impurities in the water and the amount of water distilled. White vinegar or a manufacturer's cleaner is used for cleaning.

Cost to purchase a distiller ranges from $250 for a small unit to over $1,450 for a large unit. The electrical cost for distillation can result in maintenance/operating costs higher than alternative treatment systems. The level of water quality desired, contamination of the water supply, costs, and available alternatives (bottled water) need to be evaluated before a distiller is purchased.

Filters

Dirt, sediment, and odors can be removed from water by using filters. Adsorption and mechanical filters are available. Carbon filters are the most common adsorption filter. Fiber filters are the most common mechanical filters.

Carbon Filters. Carbon-filtering equipment uses activated carbon to collect dissolved organic compounds that cause odors and disagreeable tastes. The typical use of carbon filters is to improve water for drinking and cooking. The longer the water is in contact with the filter, the more time the carbon has to remove impurities.

Carbon filters must be replaced regularly to avoid buildup of deposits. Cartridge replacement frequency depends on quantity of water used and the amount of carbon. If you are considering an activated carbon filter, look carefully at the cost of replacement filters and compare the average length of use per cartridge. Also, look at the ease of cartridge replacement.

Filter systems are installed at the point of use and can be mounted under the sink, on the sink, or on the faucet. Carbon filters are generally on cold water lines in kitchens or bathrooms to filter drinking water. It isn't common to have a carbon filter for the complete house water system unless a specific problem, such as radon contamination, occurs.

Fiber Filters. Fiber filters contain spun cellulose or rayon and are designed to remove suspended particles, such as turbidity (suspended sediment) in water. Line pressure forces water through the fibers. Particles are trapped in the filter material and removed from the water. Maintenance and replacement considerations are similar to carbon filters. Some fiber filters can be backwashed to remove trapped particles. Fiber filters can be used with carbon filters.

Remember, filters do not purify or soften water--they only remove some suspended particles and dissolved organic compounds that cause disagreeable odors and tastes.

Reverse Osmosis Units

A reverse osmosis (RO) unit is effective in removing a variety of inorganic chemicals, such as nitrates, calcium, and magnesium. A reverse osmosis unit is up to 95 percent effective. Unfortunately, reverse osmosis also removes beneficial chemicals (fluoride). Typically, a reverse osmosis unit is used to treat water used only for drinking and cooking.

An RO system typically includes:

  1. A prefilter to remove sediment.
  2. An activated carbon filter to remove odors and taste.
  3. A semi-permeable membrane through which water flows under pressure.
  4. A tank to hold the treated water.
  5. A drain connection for discharging concentrated contaminants.

Different sizes are available. They can be under the sink or in a remote location, depending on the size of the water-holding tank. The capacity of the RO system, in gallons per day, would need to be matched to household water needs. Most households find 5 gallons per day adequate.

A reverse osmosis unit is expensive (typically $600 to $900), and renting is an option. There are maintenance costs, because the RO membrane needs replacing according to the manufacturer's recommended schedule. The cost of a unit needs to be weighed against the type and quantity of contaminants in the water and the concern for safety. Further, compare the cost of an RO unit to other alternatives, such as bottled water.

Water Softeners

Hardness minerals in water can have a large effect on the home. Hard water is caused by dissolved calcium and magnesium in the water. Hard water interferes with laundering, washing dishes, bathing, and personal grooming. It also affects appliances. For example, scale builds up in water heaters, increasing the costs of heating water and reducing the life of the appliance.

The calcium and magnesium that cause hardness are reported as grains per gallon, milligrams per liter (mg/L), or parts per million (ppm). Hard water, when used with soap, causes soap deposits that will not dissolve.

Water is softened by passing through a bed of ion-exchange resin. The softening process exchanges calcium and magnesium ions in the water for sodium ions in the resin. Approximately 15 mg of sodium are added per gallon for each grain of hardness reduced.

When the sodium is exhausted, the softener needs to be regenerated. This is done by backwashing to clean the ion-exchange material, brining with salt (sodium chloride) to replace the sodium ions, and rinsing to remove any excess salt.

A water softener removes small amounts of dissolved iron (5 to 10 ppm). However, if there is oxidized iron or iron bacteria in the water, the ion exchange resin becomes coated or clogged and loses its softening ability. In this case, another method of iron removal is needed (iron filter or chlorination).

The size of a water softener depends on the hardness of water before softening, the quantity of water to be softened, and length of time between recharging. There are three types of ion-exchange softeners for the home.

Manual. Each step for recharging the unit must be activated by hand. Salt is added directly to the single tank of this softener.

Semi-automatic. The homeowner sets the system switches when recharging is necessary. The system completes the process without need for further attention. A second tank is required for brine solution.

Automatic. All steps of the recharging process are controlled by a timing mechanism that the homeowner sets, based on water usage. Some models can measure water usage or remaining softening capacity and recharge themselves only when needed. Most water softeners have a fully automatic recharging feature. These softeners also require a second tank for the brine solution.

Water softeners can be installed in various ways. The most typical installation is to soften hot and cold water, but to bypass outside water lines. This gives the fullest benefit from soft water.

The increased sodium in softened water is a concern of individuals on a sodium-restricted diet. Therefore, some water softener installations bypass the cold water line in the kitchen only.

Water softeners can be rented or purchased. Renting a softener or ion-exchange resin tank is convenient since the user does not worry about maintenance or regeneration. The dealer regularly replaces the ion-exchange resin tank; therefore, a second tank for the brine solution for recharging is not needed.

A water softener can cost $500 to over $1,500, but owning the equipment could be more economical than renting in the long run.

The cost of the water softener is balanced against the savings of soft water. Using soft water reduces the quantity of cleaning products needed by as much as 50 percent. The lives of the home's plumbing system and water-using appliances are extended. Other benefits include the time saved in cleaning and removing scale and better results in laundry, dish washing, and personal grooming.

U.S. Environmental Protection Agency
1200 Pennsylvania Avenue, NW
Washington, DC 20460
www.epa.gov