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|Sediment filters are used to remove suspended matter such as sand, silt, loose scale, clay or organic
material from the water. Untreated water passes through a filter medium and suspended matter is
trapped on the surface or within the filter medium. This guide discusses the principles, processes, and
requirements of cartridge sediment filtration systems for the household user.
What contaminants are removed from water by cartridge sediment filtration?
A cartridge sediment filter removes suspended material such as sand, silt, loose scale, clay or organic
material from the water. These materials can be the cause of turbidity or cloudiness in the water.
Sediment filters also can remove insoluble (not dissolvable) or suspended iron and manganese.
Sediment filters often are used in combination with another drinking water treatment method for
removal of contaminants such as dissolved iron, manganese or hydrogen sulfide. For instance,
sediment filters often are used after aeration, ozonation or chlorination. These treatments oxidize
dissolved iron, manganese or hydrogen sulfide into solid particles that the filter then traps. Sediment
filters also are used as prereatment for other processes such as activated carbon (AC) filtration and
reverse osmosis (RO) in order to increase their effectiveness.
What contaminants are not removed by sediment filtration?
No one piece of treatment equipment manages all contaminants. All treatment methods have
limitations and often situations require a combination of treatment processes to effectively treat the
water. Sediment filters alone do not effectively remove dissolved organic or inorganic material that
may be harmful. They do not effectively remove nitrate, heavy metals, pesticides or trihalomethanes
(by-products sometimes formed during drinking water chlorination). Cartridge sediment filters are not
generally recommended for removing microbial contaminants. Occasionally drinking water may
contain very fine suspended material, sometimes referred to as "flour sand," or very fine clay
particles, which may be too small to be removed by typical sediment filtration but may be more
effectively removed by another process such as microfiltration. See the section on treatment
principles later in this guide for further discussion.
Regardless of the water treatment system being considered, the water first should be tested to
determine what substances are present. Public water systems routinely are tested for contaminants.
Water utilities are required to publish Consumer Confidence Reports (CCRs), which inform consumers
on the source of the water, contaminants that are present, potential health effects of those
contaminants and methods of treatment used by the utility. Depending on the population served by
the utility, CCRs may be mailed, published in newspapers or posted on the Internet. A copy of the
CCR can be obtained by contacting the local water utility. Public supplies must conform to federal
standards established by the Safe Drinking Water Act. If contaminants exceed the Maximum
Contaminant Level (MCL), the water must be treated to correct the problem and/or another source of
water suitable for drinking must be provided.
In contrast, monitoring private water systems is the responsibility of the homeowner. Therefore
contamination is more likely to go undetected in a private water supply. Knowledge of what
contaminants may be present in the water should guide the testing, since it is not economically
feasible to test for all possible contaminants. It is essential to know what contaminants are present,
their quantities, and reasons for removal (i.e., to reduce contaminants posing health risks, to remove
tastes or odors, etc.) prior to selecting treatment methods or equipment.
Treatment principles and equipment
Cartridge sediment filters are generally Point-of-Use (POU) devices that can be installed under the
sink, attached to a tap, or used as a pre-filter for other water treatment processes to increase their
effectiveness and longevity. In some cases where sediment may be an issue with water-using
appliances such as washing machines, dishwashers or hot water heaters, sediment filters may be
Point-of-Entry (POE) devices that treat all water at its entry point into the home. In this situation POE
media filters or multimedia filters often are used. Consult a water treatment professional for guidance
on these filters.
Sediment filters consist of a housing, usually plastic, surrounding the filter medium. Filter material may
be paper, ceramic, polypropylene, string, spun cellulose, rayon, or granular media. It is wound or
corrugated around a tubular opening to form a cylinder. Wrapping or corrugating the material creates
a larger filter surface area for contact with untreated water.
In the sediment filtration process pressure from the water line forces the water through the media or
fiber wraps of the medium into the inner cylinder, which leads out of the filter to the water line.
Contaminants strained from the water are retained on the surface of the medium or are trapped within
it. The size of particles retained depends on the pore size or the space between media fibers or
granules. Most filters list an average pore size and are rated by the manufacturer according to the
smallest particle they can trap. For example, a 10 micron (ten thousandths of a millimeter) filter would
trap contaminants 10 microns in diameter or larger. The filter rating should be checked before
purchase since many filters are only rated for particles 20 microns in diameter or larger. Filters with
this rating may not effectively remove some silt particles, which generally range from 2.0-50 microns.
However, it would trap sand particles which generally range in size from 50 microns to 2 millimeters.
Filter pore sizes that are larger than a targeted contaminant will allow that contaminant to pass
through. For example, some very fine suspended material, sometimes referred to as "flour sand," is
too fine to be removed by many cartridge sediment filters. Some clay particles, which generally range
from 0.2-2.0 microns, are also too small to be removed by typical cartridge sediment filtration. A
microfiltration process which uses a membrane with smaller pore sizes to remove particles of 0.02-2.0
microns may be more effective in such a situation. Microfiltration removes small amounts of
suspended material and is not intended for removing a large load of material.
If the pore size of the filter medium is too small or if the concentration of suspended solids in the water
is too high, the filter may become clogged easily and require frequent replacement. In general, the
largest rating size that will remove the intended contaminants will require the least maintenance.
Figure 1 shows the sediment filtration process -- click to enlarge.
Water flow through a filter is greatest when a new or replacement cartridge is installed. As trapped
material accumulates in the filter it increases the effectiveness by assisting in the filtration process.
Water flow gradually decreases as trapped material continues to accumulate and eventually the filter
medium must be replaced. When a noticeable drop in water flow through the filter occurs, the
cartridge should be cleaned or replaced. Some cartridge filters are rated according to the number of
gallons of water they can treat. While this may be a helpful guideline, differences in the type and
amount of contaminants in the water make it difficult to accurately predict how much water a filter will
When selecting a sediment filtration device, you should determine the flow rate produced at
household water pressure (30 pounds per square inch is typical household water pressure), the
estimated amount of water treated before maintenance, and the desired water quality. The
manufacturer should provide information on the initial flow rate through the device at a given water
Plastic housings for different filters often look about the same. The filter material in the housing
determines the function and effectiveness of the filter. Information on this material should be
examined completely to be certain the correct type of filter is being purchased. In some cases bacteria
can accumulate on filters, particularly those with a paper medium. Though these bacteria may not
cause illness, they can contribute to other water quality problems such as offensive taste or odor and
corrosion. If bacterial growth occurs on a paper media filter, consider using a filter with a
non-biodegradable media material.
Federal, state or local laws do not regulate sediment filtration POU and POE home systems. The
industry is self-regulated. The NSF (formerly known as the National Sanitation Foundation) and the
Water Quality Association (WQA) evaluate performance, construction, advertising and operation
manual information. The NSF program establishes performance standards that must be met for
endorsement and certification. The WQA program uses the same NSF standards and provides
equivalent American National Standards Institute (ANSI) accredited product certifications. WQA
certified products carry the Water Quality Association Gold Seal. Though these certifications and
validations should not be the only criteria for choosing a sediment filtration system, they are helpful to
ensure effectiveness of the system.
It is possible that some water supplies may contain contaminants not addressed here, such as
cryptosporidium, giardia, hexavalent chromium and others; these are less likely to be removed by
conventional cartridge filters.
Drinking water treatment using sediment filtration is one option for a homeowner to treat home water
problems. Sediment filtration is an effective method for reducing turbidity in water caused by the
presence of suspended solids such as sand, silt, or clay. Sediment filters are also commonly used in
combination with other processes such as activated carbon filtration, aeration, ozonation or
chlorination. Selecting a sediment filtration unit should be based on water analysis and assessment of
the individual homeowner's needs and situation. Regular replacement of the filter/cartridge is a critical
factor in maintaining effectiveness and reducing bacterial contamination of the filter. The NSF and the
WQA test and certify products and this certification can help guide selection.