WATER TERMS

term	description
HAZARDOUS RANKING SYSTEM (HRS)	The principal screening tool used by the EPA to evaluate risks to public health and the environment associated with abandoned or uncontrolled hazardous waste sites. The HRS calculates a score based on a formula which is the primary factor in deciding if the site should be on the National Priorities List, and if so, what ranking it should have in comparison to other sites on the list.
HAZARDOUS WASTE	By-products of society that can pose a substantial or potential hazard to human health or the environment when improperly managed. Possesses at least one of four characteristics (ignitability, corrosivity, reactivity, or toxicity), or appears on special EPA lists.
HEADGATE	The gate that controls water flow into irrigation canals and ditches. A watermaster regulates the headgates during water distribution and posts headgate notices declaring official regulations.
HEALTH ASSESSMENT	An evaluation of data and information gathered on the release of hazardous substances into the environment to assess any current or future impact on public health.
HEALTHY HOME	A "healthy home" is built with least-toxic building materials and is designed to support and contribute to a better indoor environment.
HEAVY WATER	Water composed of isotopes of hydrogen of atomic weight greater than 1 or of oxygen greater than 16, or both; especially water composed of ordinary oxygen and the isotope of hydrogen of atomic weight 2; deuterium oxide (D2O).
HEAVY WATER MODERATED REACTOR	A reactor that uses heavy water as its moderator. Heavy water is an excellent moderator and thus permits the use of inexpensive (unenriched) uranium as a fuel.
HIGH QUALITY DUCT SYSTEM	this method of designing and installing ductwork avoids potentially significant heating and cooling losses and potential health hazards caused by depressurizing or pressurizing a house. Manuals J and D calculations are used to engineer the system. All ducts are sealed using a fibrated latex mastic and fiberglass tape, or metal tape meeting SMACNA standard 181. Both inner and outer linings of the duct are sealed. The air handler, support platform, and return plenum are sealed air tight at all joints. Duct tape is not used in any part of the system. The system can be performance tested to ensure proper installation.
HOT ROCK RESERVOIR	A potential source of geothermal power. The Òhot rockÓ system requires drilling deep enough to reach heated rock, then fracturing it to create a reservoir into which water can be pumped. This technique has not yet been perfected.
HUMIDITY	The condition of the atmosphere in respect to its content of water vapor.
HYDRAULIC RAM	A device which uses the energy of falling water to force a small portion of the water to a height greater than the source.
HYDRO	The prefix denoting water or hydrogen.
HYDROCARBONS	Chemical compounds that consist entirely of carbon and hydrogen such as petroleum, natural gas, and coal.
HYDROELECTRIC	Having to do with production of electricity by water power from falling water.
HYDROELECTRIC PLANT, CONVENTIONAL	A hydroelectric power plant which utilizes stream flow only once as the water passes downstream, as opposed to a pumped storage plant which recirculates all or a portion of the stream flow in the production of power.
HYDROELECTRICITY	Electric energy production by water powered turbine generators.
HYDROGEN	A chemical substance found in most fuels; by itself, a colorless gas that burns quickly. It is a major component of water.
HYDROGEOLOGY	The science dealing with the occurrence, distribution, and movement of water below the surface of the earth, with a greater emphasis on geology.
HYDROGRAPH	A graphic plot of changes in the flow of water or in the elevation of water level plotted against time.
HYDROLOGIC CYCLE (WATER CYCLE)	The cycle of water movement from the atmosphere to the earth and back to the atmosphere through various processes. These processes include precipitation, infiltration, percolation, storage, evaporation, transpiration and condensation.
HYDROLOGY	The science dealing with the properties, distribution and circulation of water.
HYDROMETER	An instrument used to measure the density of a liquid.
HYDROPOWER	Power produce by falling water.
HYDROSEEDING	Dissemination of seed under pressure, in a water medium. Mulch, lime, and fertilizer can be incorporated in the spraying mixture.
HYDROTHERMAL RESERVOIR	One of three forms of geothermal reservoir systems. It consists of naturally circulating hot water or steam (Òwet steamÓ) or that which contains mostly vapor (Ò`dry steamÓ). The latter type of reservoir is the most desirable type according to present technology.
HYGROMETER	An instrument used to measure humidity.
HYGROSCOPIC WATER	Water which is absorbed from the air.
HAIL	A form of precipitation which forms into balls or lumps of ice over 0.2 inch in diameter. Hail is formed by alternate freezing and melting as it is carried up and down in highly turbulent air currents.
HARDPAN	A shallow layer of earth material which has become relatively hard and impermeable, usually through the deposition of minerals.
HARVESTED RAINWATER	The rain that falls on a roof or yard and is channeled by gutters or channels to a storage tank. the first wash of water on a roof is usually discarded and the subsequent rainfall is captured for use if the system is being used for potable water. Good quality water is available by this method in most areas.
HEAVY METALS	Metallic elements with high atomic weights, e.g., mercury, chromium, cadmium, arsenic, and lead. They can damage living things at low concentrations and tend to accumulate in the food chain.
HIGHEST AND BEST USE	The classification of water based on an analysis of the greatest needs of the future. Certain quantities are reserved for appropriation according to the classification.
HOLDING POND	A small basin or pond designed to hold sediment laden or contaminated water until it can be treated to meet water quality standards or be used in some other way.
HORIZONTAL AXIS CLOTHESWASHER	See Energy Efficient Appliance.
HUMID	Containing or characterized by perceptible moisture. Usually refers to the atmosphere.

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