Water Glossary: T

TTHMs	Total trihalomethanes. By-products of chlorination.
topsoil	The top layer of soil; topsoil can grow better crops partly because it has more organic matter (humus), allowing it to hold more water than lower soil layers.
total chlorine residual	The total amount of chlorine residual present after a given contact time in a water sample, regardless of the type of chlorine. See also residual chlorine; total chlorine.*
total coliform rule (TCR)	A rulemaking of the US Environmental Protection Agency that sets National Primary Drinking Water Regulations for total coliforms, fecal coliforms, and Escherichia coli. The rule was promulgated June 29, 1989 (54 Federal Register 27544–27568) and amended Jan. 15, 1991 (56 Federal Register 1556–1557).*
total coliforms (TC)	The group of bacteria used as warm-blooded animal fecal pollution indicator organisms of drinking water quality. Total coliforms are regulated by the US Environmental Protection Agency.*
total dissolved solids (TDS)	The weight per unit volume of filtered water. The liquid passing the filter are evaporated to dryness. The filter pore diameter and evaporation temperature are frequently specified.
total organic carbon (TOC)	A measure of the concentration of organic carbon in water, determined by oxidation of the organic matter into carbon dioxide (CO2). TOC includes all the carbon atoms covalently bonded in organic molecules. Most of the organic carbon in drinking water supplies is dissolved organic carbon, with the remainder referred to as particulate organic carbon. In natural waters, total organic carbon is composed primarily of nonspecific humic materials. Total organic carbon is used as a surrogate measurement for disinfection by-product precursors, although only a small fraction of the organic carbon will react to form these by-products. Quantitatively, total organic carbon is determined by removing interfering inorganic carbon, such as bicarbonate (HCO3-), and oxidizing the organic carbon to carbon dioxide. Typically, the carbon dioxide is then measured with a nondispersive infrared detector.*
total trihalomethanes (TTHM)	The sum of the four chlorine and bromine-containing trihalomethanes (i.e., chloroform, bromodichloromethane, dibromochloromethane, and bromoform). The US Environmental Protection Agency regulates the sum of these four species on a weight concentration basis.*
transpiration	Evaporation of water through the leaves of plants.
trihalomethanes	Organic compounds which may be harmful to health at certain levels in drinking water.
toxin	Any of various substances produced by certain plant and animal cells, including bacterial toxins, phytotoxins, and zootoxins
treatment plant	A facility for cleaning and treating freshwater for drinking, or cleaning or treating wastewater before discharging into a water body
turbidity	The state of having sediment or foreign particles suspended or stirred up in water.
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