-
Dam: A structure of
earth, rock, concrete, or other materials designed to retain water, creating
a pond, lake, or reservoir.
-
Dealkalinisation: Any process that
serves to reduce the alkalinity of water.
-
Decant: To draw off the
upper layer of liquid after the heaviest material (a solid or another liquid)
has settled.
-
Decarbonation: The process of
removing carbon dioxide from water, using contact towers or air scrubbers.
-
Decomposition: The break down
of organic matter by bacteria and fungi, to change the chemical structure and
physical appearance of matter.
-
Decreasing
block rate: Pricing
that reflects per-unit costs of production and delivery that go down as customers
consume more water.
-
Defluoridation: The removal of
fluoride from drinking water to prevent teeth damage.
-
De-foaming
agents: Chemicals
that are added to wastewater discharges to prevent the water from foaming when
it is discharged into a receiving water body.
-
Degasification: The process of
removing dissolved gasses from water, using vacuum or heat.
-
Deionisation: Process that
serves to remove all ionized substances from a solution. Most commonly is the
exchange process where cations and anions are removed independently of each
other.
-
Deionized
water: Common
industrial water used to remove contaminants from products and equipment.
-
Delivery/release: The amount of
water delivered to the point of use and the amount released after use; the difference
between these amounts is usually the same as the consumptive use. See also consumptive
use.
-
Delta: A fan-shaped
alluvial deposit at a river mouth formed by the deposition of successive layers
of sediment.
-
Demand: The numerical
expression of the desire for goods and services associated with an economic
standard for acquiring them.
-
Demineralization: A process to
remove minerals from water, usually the term is restricted to ion exchange processes.
-
Demiwater: Demineralized
water. Water that is treated to be contaminant-, mineral- and salt free.
-
Denitrification: Removal of nitrate
and nitrate product from water to produce a quality that answers common water
standards.
-
Density: The weight of
a certain amount of water. It is usually expressed in kilograms per cubic metre.
-
Dental fluorosis: Disorder caused
by excessive absorption of fluorine and characterized by brown staining of teeth.
-
Depletion: Loss of water
from surface water reservoirs or groundwater aquifers at a rate greater than
that of recharge.
-
Deposit: Something dropped
or left behind by moving water, as sand or mud.
-
Depression
storage: The
storage of water in low areas, such as ponds, and wetlands.
-
Depth filtration: Treatment process
in which the entire filter bed is used to trap insoluble and suspended particles
in its voids as water flows through it.
-
Desalination: The removal of
salts from water. The three primary types of desalination are: (1) distillation,
(2) electrodialysis processes, and (3) reverse osmosis processes.
-
Desorption: The opposite
of adsorption; the release of matter from the adsorption medium, usually to
recover material.
-
Detection
limit: The lowest
level that can be determined by a specific analytical procedure or test method.
-
Detention
time: The actual
time that a small amount of water is in a settling basin or flocculating basin.
In storage reservoirs, it means the length of time water will be stored.
-
Detergent: A water-soluble
cleansing agent, other than soap.
-
Dewater: The separation
of water from sludge, to produce a solid cake.
-
Dewatering: The deliberate
attempt to lower the ground-water level in or below land surface for selected
purposes such as agricultural, construction, mining or other activities. For
mining operation, dewatering usually is accomplished by pumping the water out
of the ground and discharging to a surface-water body. However, some dewatering
involves gravity feeding water from the surficial aquifer into a deeper aquifer
through recharge wells.
-
Diatomaceous: Consisting of
or abounding in diatoms, a class of unicellular or colonial algae having a silicified
cell wall that persists as a skeleton after death.
-
Diffuser: A component of
the ozone contacting system in an ozone generator that allows diffusion of an
ozone containing gas.
-
Diffusion: The movement
of gas molecules or aerosols into liquids, caused by a concentration gradient.
-
Digester: A closed tank
for wastewater treatment, in which bacterial action is induced to break down
organic matter.
-
Diluting
water: Distilled
water that has been stabilized, buffered, and aerated. Used in the BOD test.
-
Dioxin: Any of a family
of compounds known chemically as dibenzo-p-dioxins. Concern about them arises
from their potential toxicity and contamination in commercial products.
-
Direct run-off: Water that flows
from the ground surface directly into streams, rivers, and lakes.
-
Discharge: In the simplest
form, discharge means outflow of water. The use of this term is not restricted
as to course or location, and it can be used to describe the flow of water from
a pipe or from a drainage basin. Other words related to it are runoff, streamflow,
and yield.
-
Discharge
permit: A permit
issued by a state or the federal government to discharge effluent into waters
of the state or the United States. In many states both State and federal permits
are required.
-
Disinfectants: Fluids or gasses
to disinfect filters, pipelines, systems, etc.
-
Disinfection: The killing of
the larger portion of the harmful and objectionable bacteria in the sewage.
Usually accomplished by introduction of chlorine, but more and more facilities
are using exposure to ultraviolet radiation, which renders the bacteria sterile.
-
Disinfection
byproducts: Halogenated
organic chemicals formed when water is disinfected.
-
Dispersion: The movement
and spreading of contaminants out and down in an aquifer.
-
Displacement: Distance by which
portions of the same geological layer are offset from each other by a fault.
-
Dissolve: The process by
which solid particles mix molecule by molecule with a liquid and appear to become
part of the liquid.
-
Dissolved
air flotation (DAF):
A procedure of induced flotation
with very fine air bubbles or 'micro bubbles', of 40 to 70 microns.
-
Dissolved
oxygen (DO):
Amount of oxygen gas dissolved in a given quantity of water at a given temperature
and atmospheric pressure. It is usually expressed as a concentration in parts
per million or as a percentage of saturation.
-
Dissolved
solids: Inorganic
material contained in water or wastes. Excessive dissolved solids make water
unsuitable for drinking or industrial uses. See TDS.
-
Dissolved
solids (DS):
Very small pieces of organic and inorganic material contained in water. Excessive
amounts make water unfit to drink or limit its use in industrial processes.
-
Distillation: Water treatment
method where water is boiled to steam and condensed in a separate reservoir.
Contaminants with higher boiling points than water do not vaporize and remain
in the boiling flask.
-
Distilled
water: Water
that has been treated by boiling and condensation to remove solids, inorganics,
and some organic chemicals.
-
Diversion: The transfer
of water from a stream, lake, aquifer, or other source of water by a canal,
pipe, well, or other conduit to another watercourse or to the land, as in the
case of an irrigation system.
-
Domestic
use: The quantity
of water used for household purposes such as washing, food preparation, and
bathing.
-
Domestic
wastewater facility:
Facilities that receive
or dispose of wastewater derived principally from residential dwellings, business
or commercial buildings, institutions, and the like. Can also include some wastewater
derived from industrial facilities. May also be referred to as a municipal wastewater
facility.
-
Domestic
water use: Water
for household purposes, such as drinking, food preparation, bathing, washing
clothes and dishes, flushing toilets, and watering lawns and gardens. Also called
residential water use. The water may be obtained from a public supply or may
be self supplied. See also public supply and self-supplied water.
-
Drainage
area: Of a stream
at a specified location is that area, measured in a horizontal plane, enclosed
by a topographic divide from which direct surface runoff from precipitation
normally drains by gravity into the stream above the specified location.
-
Drainage
basin: See: Watershed.
-
Dredgeate: The material
excavated from lake, river, or channel bottoms during dredging.
-
Dredging: The removal of
material from the bottom of water bodies using a scooping machine. This disturbs
the ecosystem and causes silting that can kill aquatic life.
-
Driller's
well log: A log
kept at the time of drilling showing the depth, thickness, character of the
different strata penetrated, location of water-bearing strata, depth, size,
and character of casing installed.
-
Dripstone: Deposits of calcium
carbonate that include stalactites, stalagmites, columns, and cave pearls.
-
Drop tubes: Devices that
can be added to a center pivot system to achieve greater efficiency in agricultural
irrigation.
-
Drought: Although there
is no universally accepted definition of drought, it is generally the term applied
to periods of less than average precipitation over a certain period of time.
In south Texas ranchers say drought begins as soon as it stops raining.
-
Dry cooling: Cooling-down
process using steam, to eliminate the loss of water.
-
Dry deposition: Emissions of
sulfur and nitrogen oxides that, in the absence of water in the atmosphere (i.e.,
rain), settle to the ground as particulate matter.
-
Duplicates: Two separate
samples with separate containers taken at the same time at the same place.
-
Dyke: An artificial
embankment constructed to prevent flooding.
-
Dystrophic
lakes: Acidic
bodies of water that contain many plants but few fish, due to the presence of
great amounts of organic matter.
