Glossary of Water Treatment Terms & Definitions - R

Radium

Naturally occurring radioactive elements such as radium 226 and radium 228 created in the decay of the uranium and thorium series. It can be removed from water by cation exchange softening.

Radon

A short lived radioactive gas produced from decaying uranium that is soluble in water. Can be effectively removed by activated carbon filtration or serration. Radon is considered carcinogenic when inhaled by humans.

Raw Water

Untreated water from wells or from surface sources or any water before it reaches a water treatment device or process.

Reactivation (Revivification)

Oxidation processes for restoring the adsorptive properties of a spent sorbent such as activated carbon.

Redox

A shortened term for oxidation-reduction. A reaction where electrons are gained or lost and new elements are formed.

Regenerant

The solution used to restore the activity of an ion exchanger. Acids are employed to restore a cation exchanger to its sodium form. The anion exchanger may be rejuvenated by treatment with an alkaline solution. Potassium permanganate is used to regenerate a manganese greensand iron and manganese iron and manganese removal filter.

Regeneration

The process of returning the sodium ions to the mineral after it has exchanged all its sodium ions for calcium and magnesium from hard water. This is accomplished by first back-washing the mineral bed to free it of all foreign matter, them passing salt brine through the mineral. The sodium ions attach themselves to the mineral, and the calcium and magnesium combine with the chloride from the brine to form calcium and magnesium chlorides, which are rinsed down the drain. All water softeners using the ion-exchange process are regenerated with these basic steps. In similar fashion cation and anion components of a demineralizer as well as manganese greensand are recharged with comparable sequences.

Rejection

In crossflow membrane filtration and deionization, it is the ability of the membrane to reject the passage of dissolved solids and other contaminants into the product water.

Residual

The amount of a specific material remaining in the water following a water treatment process. It may refer to material remaining as the result of incomplete removal such as hardness leakage, or to a substance meant to remain in the treated water such as residual chlorine.

Resin

Synthetic organic ion exchange material, such as the high capacity cation exchange resin widely used in water softeners. Technical name- sulfonated co-polymer of styrene and divinyl benzene.

Retentivity

The ability of an adsorbent to resist desorption of an adsorbate.

Reverse Deionization

The use of an anion exchange unit ahead of a cation exchange unit- in that order- in a deionization system.

Reverse Osmosis

A process for the removal of dissolved ions from water, in which pressure is used to force the water through a semi-permeable membrane, which will transmit the water but reject most other suspended and dissolved materials. It is called reverse osmosis because mechanical pressure is used to force the water to flow in the direction that is the reverse of natural osmosis, namely from the dilute to the concentrated solution.

R.O.

The abbreviation for "reverse osmosis".

Rust (ferric oxide)

A reddish product of corrosion sometimes found in water. Rust is formed as a result of electrochemical interaction between iron and oxygen in the presence of moisture.

The telltale rust and black colored stains on sinks, toilets and showers, strong metallic taste and impossible laundry are clear signs that you have iron or manganese in your household's water. Iron and manganese sometimes occur in water together and are sometimes accompanied by their very unwelcome friend, the rotten egg of the water world, hydrogen sulfide gas (H2S).

These culprits take on different forms and must be properly identified in order to choose the proper system for effective removal.