Introduction to Desalination. Louis Theodore

and contaminants from products and equipment.

       Riptide – A strong surface current of short duration flowing outward from the shore.

       River basin – The land area drained by a river and its tributaries.

       River bed – The bottom of a river.

       Runoff – The water from precipitation that exceeds an areas infiltration and storage that flows over the ground into a surface water body.

       Rural area – The area outside the limits of any city, town, village, or other designated residential or commercial area.

       Saline water – Water that generally is considered unsuitable for human consumption or for irrigation because of its high content of dissolved solids, generally greater than 10,000 mg/L of dissolved solids; 35,000 mg/L dissolved solids is normally assigned to seawater.

       Salinity – The amount of salts or minerals dissolved in water.

       Salinization – A process in which a soluble salt accumulates in soils.

       Salt – A chemical compound formed when the hydrogen ion of an acid is replaced by a metal, or when an acid reacts with a base in an aqueous solution.

       Salting out – A reduction in the water solubility of certain molecules in a solution of very high ionic strength.

       Saltwater intrusion – The displacement of fresh groundwater by higher density salt water near coastal regions.

       Sample – A representative specimen of a liquid, solid, or gas collected for the purpose of determining its composition.

       Sampling – A method employed to obtain representative test samples; it consists of the collection, isolation, and the possible concentration of a small fractional part of a larger volume of a media.

       Sand bar – A ridge of sand built up by deposition to the surface or near the surface of a river or along a beach.

       Sand dune – A mound or ridge of loose sand blown by prevailing winds.

       Sanitary survey – An on-site review of water sources, facilities, equipment, operation, and maintenance of a public drinking water system to evaluate the adequacy of those components for producing and distributing safe drinking water.

       Saturated rock – A rock that has all of its void spaces filled with fluid.

       Saturated soil – A soil that has all of its void spaces filled with fluid.

       Saturated zone – A subsurface soil or rock zone in which all the interstices or voids are filled with water.

       Saturation temperature – The minimum temperature at which air is saturated with water vapor; the boiling point of water.

       Scour – The action of a flowing liquid as it erodes and carries away material on the sides or bottom of a channel.

       Screening – The use of screens to separate and remove coarse floating and suspended solids from water.

       Sea – A large body of saltwater, second in rank to an ocean, that is generally part of, or connected to an ocean at some point.

       Sea level – The surface of the sea that is employed as a reference for elevation.

       Seawall – A coastal wall built to provide protection against erosion and/or flooding from the ocean.

       Seawater intrusion – The movement of seawater into freshwater aquifers near the coast when these freshwater aquifers are over pumped.

       Secondary drinking water regulation – A regulation that sets a maximum acceptable level for contaminants that adversely affect the taste, odor or appearance of water or otherwise adversely affect the public welfare.

       Sediment – The solid material or deposits that have settled from a fluid.

       Sedimentation tank – A tank in which water or wastewater containing settleable solids is retained for a period of hours to allow these solids to move to the bottom of the tank by gravity; the settled solids are removed from the bottom and the floating solids are skimmed off the top for further treatment and disposal; also called clarifiers. See also Settling tank.

       Semiconfined aquifer – An aquifer that is partially confined by a layer (or layers) of low permeability soil or rock through which recharge and discharge nevertheless may occur.

       Semipermeable membrane – A membrane that allows substances of a certain size to pass through it while preventing the passage of larger ones.

       Settleable solids – The materials that are of sufficient size and density to sink to the bottom of a sedimentation tank.

       Settling tank – A tank used in water and wastewater treatment to hold water for a period of hours, during which heavier particles sink to the bottom for removal, treatment, and disposal; also called a clarifier. See also Sedimentation tank.

       Sewage – The wastewater produced by residential, commercial, institutional, and industrial facilities.

       Sewer – The system of pipes or conduits employed to collect and deliver wastewater to treatment plants or storm water surface water bodies.

       Shore – The land bordering any body of water.

       Slow sand filtration – A treatment process that involves the passage of raw water through a bed of sand at low velocity which results in the substantial removal of chemical and biological contaminants through the development of a biolayer (schmutzdecke) at the sand surface.

       Sludge – The thick, semisolid waste that accumulates as a result of the chemical coagulation, flocculation, and settling which occurs during drinking water treatment; the thick, semisolid biomass that is produced in the biological treatment of wastewater.

       Sludge cake – The dewatered sludge from a treatment plant that has a solids content of 18 to 30% solids.

       Sludge dewatering – The process of removing water from sludge using methods such as air drying, pressure filtration, vacuum filtration, centrifugation, or belt presses.

       Sludge dryer – A mechanical device for the removal of a large percentage of moisture from sludge by heat.

       Sludge filter – Mechanical devices in which wet sludge, usually conditioned by a coagulant, is dewatered by means of vacuum (vacuum filter) or elevated pressure (pressure filter).

       Slurry –A high solids content mixture of particulate matter and liquid.

       Sodium chloride (NaCl) – A colorless, transparent, crystalline solid or white, crystalline powder; it is noncombustible.

       Soft water – A water with a low concentration of divalent, primarily calcium and magnesium, cations.

       Softening – The chemical precipitation of divalent cations which cause the hardness of water; chemical coagulants, alum or ferric chloride, are normally used as coagulants, with flocculation and sedimentation following coagulant addition.

       Soil drainage – The removal of excess water from a soil by gravity.

       Soil moisture – Water content in the soil, generally given as volume or weight percent.

       Solubility – The ability of one substance to be dissolved by another.

       Spray irrigation – The application of water to a land surface via spray droplet application.

       Steam drum – A vessel in a boiler in which the saturated steam is separated from the steam–water mixture and into which the feedwater is introduced.

       Still – An apparatus to purify liquids through heating to selectively boil and then cool to condense the vapor (e.g. to prepare alcoholic beverages, distilled water, etc.).

       Storm