431hardness of water is the lather/froth test: soap or toothpaste, when agitated, lathers easily in soft
water but not in hard water. More exact measurements of hardness can be obtained through a
wet titration. The total water 'hardness' (including both Ca2+ and Mg2+ ions) is read as parts per
million or weight/volume (mg/L) of calcium carbonate (CaCO3) in the water. Although water
hardness usually only measures the total concentrations of calcium and magnesium (the two
most prevalent, divalent metal ions), iron, aluminum, and manganese may also be present at
elevated levels in some geographical locations.
HARDNESS: A measure of the amount of calcium and magnesium salts in water. More calcium
and magnesium lead to greater hardness. The term "hardness" comes from the fact that it is hard
to get soap suds from soap or detergents in hard water. This happens because calcium and
magnesium react strongly with negatively-charged chemicals like soap to form insoluble
compounds.
HARTSHORN: The antler of a hart, formerly used as a source of ammonia. Ammonium
carbonate.
HAZARDS OF POLYMERS: Slippery and difficult to clean-up are the most common hazards
associated with the use of polymers in a water treatment plant.
HEAD: The measure of the pressure of water expressed in feet of height of water. 1 PSI = 2.31
feet of water or 1 foot of head equals about a half a pound of pressure or .433 PSI. There are
various types of heads of water depending upon what is being measured. Static (water at rest)
and Residual (water at flow conditions).
HEADWORKS: The facility at the "head" of the water source where water is first treated and
routed into the distribution system.
HEALTH ADVISORY: An EPA document that provides guidance and information on
contaminants that can affect human health and that may occur in drinking water, but which the
EPA does not currently regulate in drinking water.
HEAT: Energy transferred from one system to another by thermal interaction.
HERTZ: The term used to describe the frequency of cycles in an alternating current (AC) circuit.
HETEROTROPHIC PLATE COUNT: A test performed on drinking water to determine the total
number of all types of bacteria in the water.
HF: The molecular formula of Hydrofluoric acid.
HIGH TURBIDITY CAUSING INCREASED CHLORINE DEMAND: May occur or be caused by
the inadequate disinfection of water.
hydraulic conductivity: A primary factor in Darcy’s Law, the measure of a soil or formations ability
to transmit water, measured in gallons per day (gpd) See also Permeability and Darcy’s Law.
HYDRIDES: Hydride is the name given to the negative ion of hydrogen, H. Although this ion
does not exist except in extraordinary conditions, the term hydride is widely applied to describe
compounds of hydrogen with other elements, particularly those of groups 1–16. The variety of
compounds formed by hydrogen is vast, arguably greater than that of any other element. Various
metal hydrides are currently being studied for use as a means of hydrogen storage in fuel cell-
powered electric cars and batteries. They also have important uses in organic chemistry as
powerful reducing agents, and many promising uses in hydrogen economy.
HYDROCHLORIC AND HYPOCHLOROUS ACIDS: HCL and HOCL The compounds that are
formed in water when chlorine gas is introduced.
HYDROFLUOSILICIC ACID: (H2SiF6) a clear, fuming corrosive liquid with a pH ranging from 1 to
1.5. Used in water treatment to fluoridate drinking water.
HYDROGEN SULFIDE OR CHLORINE GAS: These chemicals can cause olfactory fatigue.
Hydrologic Cycle: (Water Cycle) The continual process of precipitation (rain and snowfall),
evaporation (primarily from the oceans), peculation (recharge to groundwater), runoff (surface
water), and transpiration (plants) constituting the renew ability and recycling of each component.
HYDROPHOBIC: Does not mix readily with water.
HYGROSCOPIC: Absorbing or attracting moisture from the air.
HYPOCHLORITE (OCL-) AND ORGANIC MATERIALS: Heat and possibly fire may occur when
hypochlorite is brought into contact with an organic material.
HYPOLIMNION: The layer of water in a thermally stratified lake that lies below the thermocline,
is noncirculating, and remains perpetually cold.