Drinking Water Treatment Systems

Public water suppliers must meet federal and state safe drinking water criteria to ensure water is safe to drink without additional treatment. Public water suppliers must notify consumers if a contaminant affecting health is found to exceed the criteria. In some cases, the supplier may be required to provide an alternate water supply. Private water supplies, on the other hand, are not regulated or tested. Individuals with private wells are responsible for protecting the water supply from contamination, testing the water quality, and selecting treatment if needed.

To select an appropriate treatment system, a builder should know which contaminants or water properties the treatment system will address. There is no single device or method that removes all contaminants or solves every water problem, and no single test to determine if water requires treatment. Though most water treatment dealers can provide free in-home or laboratory tests, the tests normally are for nuisance contaminants such as hardness, pH, iron, manganese, sulfur, and total dissolved solids. Occasionally, a dealer may test for nitrate. Seldom does any test include all the contaminants covered by the Safe Drinking Water Act (SDWA). An example of a water softener for treating hardness is shown in Figure 1.

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A water softener collects water, filters it to remove minerals, and then sends it to the home's plumbing distribution system

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Most nuisance problems such as iron, manganese, hardness, pH, and odor require treatment at the point of entry of the water in the house. Some contaminants that affect health such as nitrate and lead are a concern only for water used for drinking or cooking, so point-of-use equipment at a separate tap that treats water only where it will be used for that purpose may be adequate. Bacteria and some organic contaminants will require point-of-entry equipment to prevent exposure during bathing or other water uses.

Most residential drinking water treatment systems are at or close to 100% efficient. This means that one gallon of usable water is produced for every gallon of water that is treated, so they easily meet the 85 percent efficiency rating. One notable exception is reverse osmosis treatment systems. While useful for many reasons, reverse osmosis treatment inherently involves some amount of reject water that is not able to permeate the membrane. So it is important to confirm that these system meet the 85 percent efficiency rating, meaning that at least 0.85 gallons of usable water is produced for every gallon of water treated.

NSF International has developed the following standards that apply to drinking water treatment systems:

• NSF/ANSI 42 Drinking Water Treatment Units – Aesthetic Effects
• NSF/ANSI 53 Drinking Water Treatment Units – Health Effects
• NSF/ANSI 55 Ultraviolet Microbiological Water Treatment Systems
• NSF/ANSI 58 Reverse Osmosis Drinking Water Treatment Systems
• NSF/ANSI 62 Drinking Water Distillation Systems

Products that have been tested or evaluated by NSF to meet the minimum requirements are entitled to display the NSF listing mark on the products or in advertising literature for products. Models that meet the applicable standard are included in a listing published twice annually.

Visit the NSF website to find certified models: https://basc.pnnl.gov/library/list-nfpa-codes-standards.