Saturation. The condition of a liquid when it has taken into solution the maximum
possible quantity of a given substance at a given temperature and pressure.
Scale. An accumulation of solid material, precipitated out of waters containing certain
mineral salts in solution, and formed on the interior surfaces of pipelines, tanks, boilers,
etc., under certain physical conditions.
Secondary Maximum Contaminant Level. The advisable maximum level of a
contaminant in water that is delivered to the free-flowing outlet of the ultimate user of a
public water system. Contaminants added to the water under circumstances controlled
by the user, except those resulting from corrosion of piping and plumbing caused by
water quality, are excluded from this definition.
Secondary Regulations. Standards dealing with the esthetic quality of drinking water,
which are not federally enforceable and are intended as guidelines for the states.
Sedimentation. Process of subsidence and deposition by gravity of suspended matter
carried by water or other liquids. Also called settling, it is usually accomplished by
reducing the velocity of flow of the liquid below the point where it can transport the
Sedimentation Basin. A structure designed to hold water in a quiescent state or at a
reduced velocity for a sufficient interval of time to permit the gravitational depositing of
suspended matter, with or without the aid of previous flocculation or coagulation.
Settling basin. Settling tank.
Self-Purification. The natural process of purification in a moving or still body of water
whereby the bacterial content is reduced, the organic content is stabilized, and the
dissolved oxygen returned to normal.
Sequestering Agent. A chemical that causes the complexing of certain phosphates with
metallic ions in solution so that the ions may no longer be precipitated.
Hexametaphosphates are an example.
Service Connection. Any pipeline, with its appurtenances, which branches off or
connects with a water main and carries water from the main to a consumer.
Silting, Reservoir. The reduction of storage capacity in reservoirs due to the deposition
Slake. To mix with water. For example, when calcium oxide (unslaked lime) is mixed
with water, calcium hydroxide (slaked lime) is formed.
Sludge Dewatering. The process of removing a part of the water in sludge by any
method such as draining, evaporation, pressing, vacuum filtration, centrifuging,