The diameter of the largest hard spherical particle that will pass through a filter under test conditions.  This is an indication of the largest opening in the filter.

 The process of one substance actually penetrating into the structure of another substance.

Chemicals that are low in pH. Of primary concern is the deleterious effect most acids may have on filter medium and housings.

The physical process occurring when liquids, gases or suspended matter adhere to the surface of, or in the pores of, an adsorbent medium. Adsorption is a physical process which occurs without chemical reaction.

Plant-like organisms which grow in water.


The reverse flow of water through a filter, used for removing solids accumulated during the filtration process.

Microbial organisms that Lives in soil, water, organic matter or the bodies of plants and animals and being autotrophic (self-generative), saprophytic or parasitic.

The amount of oxygen needed by aerobic biological organisms in a body of water to break down organic material present in a given water sample at certain temperature over a specific time period.

Water containing dissolved solids in the range > 1,000 to < 15,000 ppm – salinity levels between freshwater and seawater.


Fine, hair like tube having a very small opening.

Any removable pre-formed or pre-packaged component containing a filtering medium, ion exchanger, membrane or other treatment material which fits inside a housing to make up a cartridge filter.

A test is commonly used to indirectly measure the amount of organic compounds in water – expressed in milligram per liter.

Foreign matter in a fluid, which is usually undesirable.  Contaminants may cause discoloration or haze in a liquid, abrasion or wear on surfaces, system upsets in process systems, disease in living things.  Contaminants are the reason why filtration is necessary.


Type of filters that use a porous filtration medium (usually grains or fibers) to retain particles throughout the medium, by means of their interception and adhering to the filtration media, rather than just on the surface of the medium.

The removal of dissolved inorganic solids (salts) from solution such as water to produce a liquid which is free of dissolved salts. Desalination is typically accomplished by distillation, reverse osmosis or electrodialysis.

Defined as the difference in pressure between the inlet side of the filter, and the outlet side of the filter.


The area of a medium that is exposed to flow and usable for filtering.  Opposite of blind spots or dead area.

percent of contaminant reduction which occurs with a specified medium volume and specified water contact time.


device installed as part of the water system through which water flows for the purpose of removing particles, turbidity, taste, color, iron or odor by means of a physical barrier, chemical or biological process.

The total area of a filter element.

The mechanical or physical operation which is used for the separation of solids from fluids by interposing a medium through which only the fluid can pass.

The flow rate divided by the cross sectional area of the filter.

The rate at which a quantity of water passes a given point in a specified unit of time.


A common waterborne protozoan that forms cysts. The cysts are approximately 8um X 12um in size and can be removed from water by filtration (below 5 micron). The infection causes considerable gastric discomfort and it usually requires treatment by a physician.

Gallons per minute.

Water found beneath the surface of the ground (also referred as Well Water)


The stream of water to be treated as it flows into any kind of water treatment unit or device, such as turbid water into a filter. (also referred as Feed Water).

Substances which do not formed from living substance; those substances which do not contain carbon as a major constituent.


Species of bacteria, such as Legionella pneumophila, which can cause pneumonia-like illness called “Legioella Disease”. These bacteria are known to thrive at 37º C (100º F).


A thick layer of graded particles such as sand, gravel or other granular materials used to perform the filtration of a liquid. Multiple different layers of materials may be used to form the filter bed.

Polymer film of microporous structure, either natural or man-made, utilized as the semipermeable separation mechanism in reverse osmosis, ultrafiltration and microfiltration.

Number of openings, or fractions of openings, in a lineal inch of wire cloth / screen element.

The removal from a liquid of particles and microorganisms in the size range of 0.1 to 2.0 microns in diameter (other consider particle size used for microfiltration ranges from 0.1 up to 10 µm).

A short unit of length in the metric system: one thousandth of a millimeter. Used as a criterion to evaluate the performance of efficiency of a filter or to describe the condition of either the influent or effluent.


a relatively recent membrane filtration process used most often with low total dissolved solids water. Falls between reverse osmosis and ultra filtration on the filtration spectrum.

Nominal micron rating is generally taken to mean that 98% of all particles over a given micron value have been removed by a specific media or medium.

Nephelometric Turbidity Unit. The units of turbidity from a calibrated nephelometer. Measure of turbidity in water by the propensity of particles to scatter a light beam focused on them.


The normal pressure  of at which a system operates (manufacture’s specific range). Also called working pressure.

The process of feeding ozone into a water supply for the purpose of decolorization, deodorization, disinfectant or oxidation.


A tabulation resulting from a particle count of solids grouped by specified micron sizes to determine the condition of either the influent or effluent stream.  Usually expressed in percentage of total solids to the specific group.

A measure of the acidity of water. The pH scale runs from 0 to 14 with 7 being the mid-point or neutral. A pH of less than 7 is on the acid side of the scale. A pH of more than 7 is on the basic (alkaline) side of the scale.

A channel or opening in a filter that allows the passage of fluid.

A water supply which meets U.S. EPA and/or state water quality standards and is considered safe and fit for human consumption

Parts per million

Removal of coarse particles or large debris prior to a finer filtration process.

the ratio of force to the area over which that force is distributed.

Pounds per square inch (pressure unit).


Water which has had no previous treatment and is entering the water processing system or device.

A natural or artificial lake / pond which is used to store water

A water separation technology that uses a semipermeable membrane to remove many types of molecules and ions from solutions. It is used in both industrial processes and the production of potable water. This process is called “reverse” osmosis because the pressure forces the water to flow in the reverse direction (from the concentrated solution to the dilute solution) to the flow direction in the process of natural osmosis.


The oldest and most basic depth filter filtration process, which generally uses two grades of sand (coarse and fine) for turbidity removal. Rapid and Up-flow sand filters require the use of flocculant chemicals to work effectively while slow sand filters can produce very high quality water free without the need for chemical aids.

Silt Density Index.  An ASTM standard test, for measuring the relative quantity of particulate matter in water. Used mainly as a measure for the fouling capacity of water in reverse osmosis systems.

Gravitational settling of particles suspended in a liquid.

All of the water on the surface of the earth including streams, lakes oceans, rivers, glaciers and some shallow wells that can be fed by surface runoff water.


Total Dissolved Solids. The accumulated total of all solids that dissolved in water, given in ppm per unit volume of water.

The concentration of suspended particles given in ppm per unit volume of water. This term is sometimes used to prevent confusion with measurements that include dissolved solids.

amount of small particles of solid matter suspended in water as measured by the amount of scattering and absorption of light rays caused by the particles. Turbidity is measured in nephelometric turbidity units (NTU).


The resistance to flow exhibited by a liquid resulting from the combined effects of cohesion and adhesion.  The units of measurement are the poise and the stoke.


Water that has been adversely affected in quality by prior usage.