We all know that things are getting smaller these days. Why even in the great state of Texas where things are always bigger, consumer reports show that people are turning in droves to smaller computers and tiny little cell phones. It is a trend that even has the "Big Cheese" himself—Ronald McDonald taking notice—leading the nation’s largest fast-food chain to do away with the “super-sized” value meals.
For years there has been a growing debate in the water/wastewater industry over “small,” decentralized, water treatment systems and how useful these point-of-use (POU) and point-of-entry (POE) treatment options are for small water systems, especially in the removal of arsenic.
Designed to be installed just as their name implies—POU devices are installed at the point where water is used and purify only that portion of incoming water that is being used for drinking and cooking purposes. POE devices, on the other hand, are installed at the point where water enters a household and treat all the water coming into a house or facility.
POU/POE devices have the potential to assist systems in dealing with a wide variety of contaminants, including arsenic, organic contaminants, nitrate, iron, and many other contaminants. These systems often utilize the same treatment technology used in centralized treatment—but on a much smaller scale (You should see the cute little uniforms that the system operators wear!). While some decentralized systems have the ability to treat raw water, these devices are more often used to treat finished water that may have degraded during distribution or storage.
While primarily used to deal with aesthetic concerns such as taste or odor, some small water systems that find themselves having difficulty complying with the U.S. Environmental Protection Agency (EPA) maximum contaminant level (MCL), may find that POU/POE water treatment systems can be used to provide a cost-effective alternative to more expensive centralized treatment options.
Tip: Maximum Contaminant Level (MCL) is a value defined under the Safe Drinking Water Act Section 1401(3) as the maximum permissible level (concentration) of a contaminant in water delivered to any user of a public water system.
In this issue of the Safe Drinking Water Trust eBulletin, we will take a closer look at POU/POE devices (remember, you have to look close---they’re small!) and how these alternative treatment options might help your system.
Additional Resources
www.nsf.org/business/drinking_water_systems_center/pdf/GrimesFinalReport_Dec05.pdf [1]
Regulating POU/POE Usage
The 1996 Safe Drinking Water Act (SDWA) imposes significant demands on water systems to achieve compliance, but it also provides opportunities to devise unconventional compliance approaches that are geared to the specific problems of small and very small communities.
Numerous decentralized POU treatment technologies have been shown by challenge testing and experience to have the capability to reliably reduce contaminants in drinking water to below MCLs. The SDWA even lists POU/POE systems as options for compliance technologies. However, when a water system chooses to use this type of device to comply with a National Primary Drinking Water Regulation (NPDWR) the SDWA requires that:
? Only POE treatment devices can be used to achieve compliance regarding microbial contaminants or indicators of microbial contaminants.
? POU and POE treatment devices must be owned, controlled, and maintained by the public water utility or a contractor hired by the utility to ensure their proper operation and maintenance and compliance with the MCLs. The utility must retain oversight of device installation, maintenance, and sampling and is responsible for the quality and quantity of water provided to the community.
? POU and POE treatment units must be equipped with a warning device (e.g., an alarm, a light) to alert the consumer that it is no longer functioning properly. Alternatively, there must be an automatic shutoff feature.
? Only units that have met National Sanitary Foundation (NSF) and American National Standards Institute (ANSI) standards may be used. If they are covered by these standards, they must be independently certified according to these standards by an accredited laboratory.
Buried among the pages of the SDWA, POU devices are listed as compliance technologies for inorganic contaminants, synthetic organic contaminants, and radionuclides. POU devices are not listed for volatile organic contaminants because they do not address all routes of exposure.
When POU/POE are installed in order to meet regulatory compliance, the water utility bears the responsibility to properly install, maintain, and monitor the device, subject to state approval. For example, the state must approve a monitoring plan prepared by the water utility when a POE device is installed for regulatory compliance. In addition, a state may require a feasibility study to justify a water system’s selection of POU or POE technology instead of an alternative means of meeting an MCL.
Despite the amendments to the SDWA allowing the implementation of POU/POE treatment, some states may prohibit or restrict a system from using these devices. Such is the case in Pennsylvania where regulatory officials currently do not allow POU treatment devices to be used to meet compliance requirements.
Additional Resources
www.nesc.wvu.edu/ndwc/pdf/OT/TB/TB_Sp03_point.pdf [2]
POU/POE Devices Provide Security
A recently released report issued by the EPA and the National Homeland Security Research Center found that POU/POE treatment devices could also provide a certain amount of water security benefits when installed at high-risk facilities such as hospitals, military bases, police stations, and fire stations.
According to the report, when used in circumstances where a limited population has been affected and the type of contamination is clearly known, prefiltration, Reverse Osmosis (RO), Carbon absorption and ultra-violet (UV) disinfection devices showed promising results.
While it is unlikely that we will see that day when centralized water treatment is abandoned for under-the-sink mounted water treatment devices, or the day when systems stockpile POU/POE devices so that they can whip them out if there is a credible threat to the security of their system, some systems, especially small ones, may find that these little devices can prove largely useful.
A recent year-long experiment conducted in the small town of Grimes, CA, found that while gaining community support and installing POU devices at 122 business and residences proved challenging, the units did provide a cost-effective method of reducing arsenic below the required MCL.
According to the study completed by the National Science Foundation, costs calculated using a projected seven-year life and a seven percent cost recovery rate showed that traditional centralized treatment would cost residents $24.31 per month, while POU treatment with all cartridges changed annually and every unit sampled once per year, the monthly cost per customer would run $14.67.
Additional Resources
www.epa.gov/ordnhsrc/pubs/reportPOUPOE022406.pdf [3]
Little Devices: Big Decisions
Since there isn’t a single type of residential water treatment system currently available that will reliably treat all water quality problems, a wide variety of POU/POE systems are currently on the market, including:
Filters: Water passes through the filter media, which either absorbs or physically screens
various contaminants.
Solid Block Activated Carbon (SBAC) is a solid compressed block of activated carbon. Can be used for odor, taste control, and to remove radon and regulated organic compounds. These can also be used to remove lead, asbestos, various bacteria, cysts, and sediment particulates. Because SBAC filters are so fine, they easily become plugged with particulate matter, and frequently need to be replaced.
Granular Activated Carbon (GAC) is composed of loose granules of carbon. These filters can be used to control odor, taste, and to remove radon and regulated organic compounds. GAC filters are know to accumulate the organic impurities they remove from the water, allowing them to become food for bacteria.
Reverse Osmosis (RO): Water passes through a semi-permeable membrane which
removes inorganic minerals like radium, sulfate, calcium, magnesium, potassium, sodium, nitrate, fluoride, and phosphorous. RO units must have a means of discharging filtered matter to a drain. RO units are often used in combination with an activated carbon filter.
Ultraviolet (UV) Light: This type of water treatment uses a mercury arc lamp to kill
pathogens in the water. UV radiation kills most bacteria and some viruses, but is ineffective against cysts and worms. Cloudy or turbid water can reduce the effectiveness of UV radiation.
Ozone: Ozone occurs naturally in our atmosphere. In fact, the ozone layer in our
atmosphere protects us from ultraviolet radiation coming from the sun. In ozonation of water, electrically generated ozone kills bacteria and some other pathogens and removes some pesticides. Ozone does not produce any taste or odor in water.
Ion Exchange (IE): An ion exchange column is one of the most common water
treatment systems found in the home. Also known as a water softener, ions of either sodium or potassium, stored in the softener’s “resin bed” are exchanged for ions of the calcium and magnesium hardness minerals. Ion exchange can be used for de-alkalization and to remove iron and manganese, heavy metals, some radioactivity, nitrates, arsenic, chromium, selenium, and sulfate.
Distillation: A distillation unit works by evaporating water and collecting the steam that
is produced. Impurities in the water are left behind. This process can remove lead, nitrate, sodium chloride, and many pesticides and organic compounds. Distilled water is often said to have a flat or bland taste due to the removal of minerals.
Deciding if a POU is Right 4U?
Traditionally, most customers are accustomed to the idea that the water pouring from their taps has been “mysteriously” made pure at some far removed treatment plant located in another part of town. Getting them to accept the idea that the water pouring forth from their faucets may need just a little more treatment can prove challenging.
In order for a system to successfully introduce the idea of installing POU/POE treatment devices, there must be a very high degree of acceptance in the community. It is also critical that the water system be dedicated from the very start to undertaking the responsibility of instituting and managing a decentralized system for the long term.
If after a great deal of research and consultation with your contacts at your state primacy agency you come to the conclusion that a POU/POE treatment program is an option for your community, then public outreach and communications are critical throughout the process. Your system—from the top down—must unite to inform citizens of the choices, determine their acceptance and willingness to participate, and keep them up to date on developments and maintain their support.
Some questions that should be addressed by water suppliers considering a POU/POE compliance system are:
? What is the contaminant and by how much does it exceed the MCL?
? Is the contaminant among those that are permitted to be treated by decentralized
methods?
? What is the composition and variability of the source water?
? What are the available technology options and how are they affected by the
characteristics of the source water?
? What are the capitol and operating costs and operating requirements of the
alternative central and decentralized options?
? Is cost recovery feasible through rates, or are subsidies available?
? How reliable is the technology and how resistant is it to changes of source
water conditions?
? What level of O&M will be required?
? What skill level is required of the operators; will it be possible for the system to
be community-managed or will a contract service provider be more appropriate?
? What is the extent of compliance monitoring and process monitoring that will
be required and what are the methods and costs?
? Will new ordinances or contracts be required to ensure participation of the
entire community and ensure access to residences by service personnel for
maintenance and monitoring?
?Will additional liability insurance be required to protect the community from
any costs due to property damage or other problems that might result from the
presence of the units or operators in the homes of consumers?
? What wastes are generated and what are the disposal options and their
associated costs?
Additional Resources
www.nrwa.org/whitepapers/risks/risks01/risks01.doc [4]
The Future of Water Treatment
Meeting SDWA regulatory compliance requirements, especially for small water systems, is always difficult due to limited technical choices, limited access to resources and trained personnel, and the lack of economies of scale when only a small volume of water is being produced and the O&M costs are spread over a small number of consumers. Under certain circumstances the SDWA allows for compliance to be achieved in small systems using POE and POU treatment units. Therefore, if there is a good possibility that a decentralized approach is feasible and cost effective, it should be considered as a potential compliance method.
However, it is clear that a decentralized treatment approach is not for everyone. One determining factor, among many, will be the size of the community. Remember, there will always be a site-specific crossover point where it is more feasible and cost effective to use a central treatment approach. In the case of Grimes, CA, a community of only 400 residents and 122 service connections, it soon became clear that a decentralized approach was the cost effective solution. However, without adequate community support, and willingness to allow access to their homes for installation, maintenance, and water quality monitoring, the cost savings would have been unimportant.
Therefore, if your community is serious about considering a decentralized water treatment program, then it is important to research the facts, start talking with your state primacy agency now, and develop a game plan so that you can deal with the issues that will arise.