Drinking Water Treatment filtering: Filters Table

Types of Treatment	How It Works	Contaminants Removed	Limitations	Maintenance/Efficiency
Activated Carbon Filtration	Water passes through a filter and contaminants absorb or adhere to the extremely porous filter. Very effective at removing bad taste and odor.	Many organic compounds, such as chlorinated and nonchlorinated solvents, some SOCs, naturally occurring organic matter, some gasoline components, and trihalomethanes. This material is also effective for removal of chlorine and moderately effective for removal of some heavy metals and metals that are bound to organic molecules. See complete list of contaminants removed.	Limited removal capability for atrazine, alachlor. Needs prefilter for sediment removal. GAC filters are prone to *channeling. Bacterial growth can be a problem.	Determine appropriate intervals of replacement based on contaminant concentration, flow rate, depth of filter, amount of AC and prefilter. Retailers can help in this analysis. Works best under low flow conditions, but those same conditions can contribute to bacterial growth.
Reverse Osmosis (RO)	RO treatment relies on water pressure to force clean water through a semipermeable membrane. Since contaminants do not move with the water as it moves across the membrane, purer water collects on the other side of the membrane.	According to data presented by the NSF most inorganic compounds of health concern are removed by certified RO systems. See RO table for complete list of contaminants removed.	"One sediment and two activated carbon filters are needed for proper operation of a reverse osmosis system. One carbon a head of the membrane to protect it from chlorine and one post as a polishing filter. Hard water can shorten the life expectancy of the membrane. RO systems should not be used to treat water that has not been sanitized. "	Activated carbon filters require regular replacement. RO systems can waste a large amount of water. The waste stream generated is pressure and temperature dependent.
Sediment Filtration	As water passes through the filter, suspended particles of relatively large size (5 to 10 microns) are trapped in and on the filter. Some typical types of filters are string wound, spun bonded polypropylene, and paper.	Dirt, sand, silt, clay, mud and other suspended contaminants. If large quantities of sand or other contaminants are present in the feed water, a back washing type filter may be placed ahead of the filter to prolong its life.	This type of filter does not effectively remove nitrates, heavy metals, pesticides or by-products formed during chlorination or microbial contaminants. In some cases, bacteria can accumulate on filters, particularly those with a paper medium.	Filters need be used regularly. Long idle periods may lead to excessive bacterial growth. Under normal use, if bacterial growth occurs on a paper media filter, consider using a filter with a non-biodegradable material.
Distillation	Water is boiled, and the steam is carried over into a condenser where it is cooled and returned as distilled water. The impurities and dissolved solids that are left behind in the boiler are drained away.	"Arsenic, copper, dissolved minerals, fungicides, lead, microorganisms, nitrates, pesticides, selenium, sodium, sulfates, volatile organic contaminants* and turbidity. Although distillation is capable of removing radium, and uranium, it is not FDA approved."	Distillation effectiveness for organic contaminants is dependent upon the performance of the VOC trap. These traps are highly energy dependent. Requires additional filters to be highly effective.	Water with high mineral content will cause excessive mineral build up and increase maintenance. High cost per gallon of production. Along with slow production, typically 5 hours to produce one gallon make this purifying method cost prohibitive for most homeowners.
Ultraviolet (UV) Radiation Disinfectant	Water flows past a high intensity light radiating in narrow bands and kills the pathogens. This process is an extremely effective disinfectant but does nothing else.	Bacteria, giardia,viruses.	Water with high turbity will need pre-filtration. This type of treatment has no lasting effect and the water could become tainted from an internal source of contamination. Does not effectively deal with giardia lambia cysts.	The lamp must be kept clean and periodically replaced to maintain effectiveness. Overall efficiency depends on the flow rate of the water, the intensity of the light, and the clarity of the feed water.
*Channeling: the water channels through the media which reduces the contact between the contaminant and the carbon and reduce efficiency