Glossary of Terms - R
A B C D E F G H I J K L M N O P Q R S T U V W Z
radon (Rn) - A colorless, odorless, short-lived radioactive gas which is produced by decay of the uranium/radium series and is soluble in water. Radon is considered carcinogenic when inhaled by humans. Radon can be removed from water by aeration or activated carbon.
rated capacity - The basis for calculating the period of time, or number of gallons delivered by a water softener, filter, or deionizer, between regenerations or servicing, as determined under specific test conditions. (See rated in-service life, rated softener capacity).
rated in-service life - The length of time or total gallons delivered between servicing of the media in a filter as determined under standard test conditions.
rated pressure drop - The pressure drop of a water softener or filter at the rated service flow, with clean water at a temperature of 60oF, with a freshly regenerated and/or backwashed softener or filter, as determined under standard test conditions.
rated service flow - The manufacturer-specified maximum and minimum flow rates at which a particular piece of water treatment equipment will continuously produce the desired quality of water.
rated softener capacity - The statement by the water softener manufacturer about the expected number of grains per gallon of total hardness (as calcium carbonate equivalent) that will be removed between regenerations at the specified flow rate using the specified amount of regenerant (usually sodium chloride). The capacity of ion exchanger resin to remove hardness increases, within limits, with higher regeneration salt dosages; therefore, rated softener capacity must be related to the pounds of salt required for each regeneration.
raw water - 1. Water, usually from wells or surface sources, which has had no previous treatment and is entering a water processing system or device.
2. Water at the inlet side of any water treatment system or device.
recovery - In reverse osmosis processes, indicates the amount of product water taken from the feed water stream; expressed as a percentage of product water flow rate to feed water flow rate.
reduction - Reduction is the addition of hydrogen, removal of oxygen, or the addition of electrons to an element or compound. Under anaerobic conditions (no dissolved oxygen present), sulfur compounds are reduced to odor-producing hydrogen sulfide (H2S) and other compounds. The opposite of oxidation.
red water - Water which has a reddish or brownish appearance due to the presence of precipitated iron and/or iron bacteria.
regenerant - In ion exchange or softening applications, a regenerant is the chemical solution used to restore an exhausted bed of ion exchange resin to the fully ionic (regenerated) form necessary for the desired ion exchange to again take place effectively. Regenerants are also used in a similar fashion to restore catalyst (e.g., iron and manganese removal) media for reuse. Sodium chloride brine is normally used to regenerate cation exchange water softeners and for some dealkalizer systems. Hydrochloric and sulfuric acids are used for hydrogen-form cation deionizations units. Sodium hydroxide is normally used to regenerate OH- form anion deionizations systems. Potassium permanganate regenerant is used to regenerate a manganese greensand iron and manganese removal filter.
regeneration - In ion exchange applications, the use of a chemical solution (regenerant) to displace the contaminant ions deposited on the ion exchange resin during the service run and replace them with the kind of ions necessary to restore the capacity of the exchange medium for reuse. This process is also called recharging or rejuvenation. Catalyst media are recharged similarly.
regeneration level - The quantity of regenerant used in the regeneration of an ion exchange unit or system, usually expressed in pounds per regeneration and/or pounds per regeneration per cubic foot of ion exchanger.
rejection - In reverse osmosis processes, the degree of removal of dissolved salts from the feed water as it passed through a semi-permeable membrane (also called "salt rejection"); expressed as a percentage of the feed water TDS. (See total dissolved solids.)
reserve capacity - The amount of further contaminant reduction or length of time a device can continue to operate at a high level of performance after a signal of upcoming exhaustion is triggered.
residual - The amount of a specific material remaining in the water following a water treatment process; may refer to material remaining as a result of incomplete removal (see leakage), or to material meant to remain in the treated water. (See residual chlorine.)
residual chlorine - Chlorine allowed to remain in a treated water after a specified period of contact time to provide continuing protection throughout a distribution system; the difference between the total chlorine added, and that consumed by oxidizable matter. (See combined available chlorine, free available chlorine.)
resin - Synthetic organic ion exchange material, such as the high capacity cation exchange resin widely used in water softeners.
resin cleaner - One of several different chemical compounds used to cleanse ion exchange resin products of dissolved iron, aluminum, and various organics attracted to or bonded to the resin beads.
resistance - In water conditioning, the opposition offered by water to the flow of electricity through it; the reciprocal of electrical conductance. The unit of measurement for electrical resistance is the Ohm. Electrical resistance can be used to approximate the mineral content, or lack of it, in high quality water. (See conductance).
resistivity - A capacity for resisting the flow of electricity. (See resistance.)
reverse deionization - The use of the anion exchange resin ahead of the cation exchange resin (the reverse of the usual order), in a deionization system.
reverse osmosis (R.O.) - A water treatment process that removes undesirable materials from water by using pressure to force the water molecules through a semi-permeable membrane. 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 (from the dilute to the concentrated) in the process of natural osmosis. RO removes ionized salts, colloids, and organic molecules down to a molecular weight of 100. May be called hyperfiltration.
rinse - That portion of the regeneration cycle of an ion exchanger in which fresh water is passed through the column to remove spent and excess regenerant, prior to placing the system in service.
R. O. - Reverse osmosis.
rust remover - A product that removes rust stains from fabrics, dishwashers, and other washable surfaces, such as bathrooms, kitchens, tea kettles, dishes and glassware, and wherever water comes in contact. Most commonly, these materials are composed of reducing agents (such as sodium hydrosulfite) or acid products, and may be in liquid, powder, or gel form. During laundering, some rust removers may be used in the regular laundry cycle or for presoaking. They may also be useful for miscellaneous stain removal, such as removal of dye-bleeding. Rust removers made to remove rust, scale, and lime deposits from the inside of dishwashers are a combination of acids. Used periodically as needed, they are added at the beginning of the main wash cycle (no dishes or other cleanser present) and are allowed to remain through the balance of the cycles.