441RESIDUAL DISINFECTION PROTECTION: A required level of disinfectant that remains in
treated water to ensure disinfection protection and prevent recontamination throughout the
distribution system (i.e., pipes).
REVERSE OSMOSIS: Forces water through membranes that contain holes so small that even
salts cannot pass through. Reverse osmosis removes microorganisms, organic chemicals, and
inorganic chemicals, producing very pure water. For some people, drinking highly purified water
exclusively can upset the natural balance of salts in the body. Reverse osmosis units require
regular maintenance or they can become a health hazard.
ROTAMETER: The name of transparent tube with a tapered bore containing a ball is often used
to measure the rate of flow of a gas or liquid.
ROTIFER: Rotifers get their name (derived from Greek and meaning "wheel-bearer"; they have
also been called wheel animalcules) from the corona, which is composed of several ciliated tufts
around the mouth that in motion resemble a wheel. These create a current that sweeps food into
the mouth, where it is chewed up by a characteristic pharynx (called the mastax) containing a
tiny, calcified, jaw-like structure called the trophi. The cilia also pull the animal, when unattached,
through the water. Most free-living forms have pairs of posterior toes to anchor themselves while
feeding. Rotifers have bilateral symmetry and a variety of different shapes. There is a well-
developed cuticle which may be thick and rigid, giving the animal a box-like shape, or flexible,
giving the animal a worm-like shape; such rotifers are respectively called loricate and illoricate.
S
S- BLOCK ELEMENTS: Group 1 and 2 elements (alkali and alkaline metals), which includes
Hydrogen and Helium.
S.T.P.: Standard temperature and pressure standard temperature and pressure the
temperature of 0°C and pressure of 1 atmosphere, usually taken as the conditions when stating
properties of gases.
SAFE YIELD: A possible consequence when the “safe yield” of a well is exceeded and water
continues to be pumped from a well, is land subsidence around the well will occur. Safe yield
refers to a long-term balance between the water that is naturally and artificially recharged to an
aquifer and the groundwater that is pumped out. When more water is removed than is recharged,
the aquifer is described as being out of safe yield. When the water level in the aquifer then drops,
we are said to be mining groundwater.
SALINE SOLUTION: General term for NaCl in water.
SALT BRIDGE: Devices used to connection reduction with oxidation half-cells in an
electrochemical cell.
SALTS: Ionic compounds composed of anions and cations.
SALTS ARE ABSENT: Is a strange characteristic that is unique to water vapor in the atmosphere.
SAMPLE: The water that is analyzed for the presence of EPA-regulated drinking water
contaminants. Depending on the regulation, EPA requires water systems and states to take
samples from source water, from water leaving the treatment facility, or from the taps of selected
consumers. Sampling Location: A location where soil or cuttings samples may be readily and
accurately collected.
SANITARY SURVEY: Persons trained in public health engineering and the epidemiology of
waterborne diseases should conduct the sanitary survey. The importance of a detailed sanitary
survey of a new water source cannot be overemphasized. An on-site review of the water sources,
facilities, equipment, operation, and maintenance of a public water systems for the purpose of
evaluating the adequacy of the facilities for producing and distributing safe drinking water. The
purpose of a non-regulatory sanitary survey is to identify possible biological and chemical
pollutants which might affect a water supply.
SANITIZER: A disinfectant or chemical which disinfects (kills bacteria), kills algae and oxidizes
organic matter.
SATURATION INDEX: See Langelier's Index.
SATURATOR: A device which produces a fluoride solution for the fluoride process. Crystal-grade
types of sodium fluoride should be fed with a saturator. Overfeeding must be prevented to protect
public health when using a fluoridation system.