Glossary of Terms - T
A B C D E F G H I J K L M N O P Q R S T U V W Z
tannins - Any of a group of water soluble, natural organic phenolic compounds that are produced by metabolism in trees and plants, and are part of the degradation - resistant fulvic acid materials formed during the decomposition of vegetation. Tannins occur in water in almost any location where large quantities of vegetation have decayed. Tannins can impart a faintly yellowish to brown color to water. Tannin molecules tend to form anions in water above pH 6 and can then be treated with anion exchange resins. Below pH 5, tannins are better treated with activated carbon.
TCE - See Trichloroethylene.
TDS - See Total dissolved solids.
TDS Creep - The appearance of salt in RO product water which sometimes occurs as a result of the reduction of differential pressure across the membrane as can occur when the RO unit has been shut down for a period of time.
Water flow will cease to permeate through the membrane when there is insufficient differential water pressure across the membrane. However TDS permeates through the membrane as a function of the TDS concentration difference across the membrane.
temporary hardness - Water hardness due to the presence of calcium and magnesium carbonates and bicarbonates, which can be precipitated by heating the water. Now largely replaced by the term "carbonate hardness". (See carbonate hardness, permanent hardness.)
threshold - The lowest dose of a chemical at which a specified measurable effect is observed and below which it is not observed.
throughput volume - The amount in gallons or liters of water passed through an ion exchange resin bed or water treatment system before exhaustion of the exchanger or system is reached.
titrate - To titrate a sample, a chemical solution of known strength is added on a drop-by-drop basis until a certain color change, precipitate, or pH change in the sample is observed (endpoint). Titration is the process of adding the chemical reagent in increments until completion of the reaction, as signaled by the endpoint.
titration - An analytical technique for determining how much of a certain substance (concentration) is present in a solution (such as a water sample) by measuring how much of another substance (of known concentration) must be added to produce a given reaction (often color change in the solution).
Titration is used for determining the level of concentration of a substance in solution. This procedure is widely used in water testing.
total acidity - The total of all forms of acidity, including mineral acidity, carbon dioxide, and acid salts in a solution. Total acidity is usually determined by titration with a standard base solution to the phenolphthalein endpoint (pH 8.3). (See acidity.)
total alkalinity - See Alkalinity.
total chlorine - The total concentration of chlorine in a water, including combined available and free chlorine. (See combined available chlorine, free available chlorine.)
total dissolved solids (TDS) - The total weight of the solids that are dissolved in the water, give in ppm per unit volume of water. TDS is determined by filtering a given volume of water (usually through a 0.45 micron filter), evaporating it at a defined temperature (usually 103-105 degrees Celsius), and then weighing the residue.
Note: A test measuring the electrical conductivity of the water provides only an estimate of the TDS present, as conductivity is not precisely proportional to the weight of an ion and nonconductive substances cannot be measured by electrical tests.
total hardness (TH) - The sum of all hardness constituents in a water, expressed as their equivalent concentration of calcium carbonate. Primarily due to calcium and magnesium in solution, but may include small amounts of metals such as iron, which can act like calcium and magnesium in certain reactions. (See hardness.)
total solids (TS) - The weight of all solids, dissolved and suspended, organic and inorganic, per unit volume of water; usually determined by the evaporation of a measured volume of water at 105oC in a pre-weighted dish.
toxic - Poisonous (to living organisms); capable of producing disease or otherwise harmful to human health when taken into the body.
trace substance (or trace) - A substance which is found during water analysis in a very small concentration high enough to be detected, but too low to be quantified accurately by standard testing methods. Sometimes referred to as a threshold substance.
transpiration - The process in which living plants release water vapor into the atmosphere, a significant part of the hydrologic cycle.
trichloroethylene (TCE) - A toxic volatile organic compound often used as a solvent.
TS - See Total Solids
tuberculation - The process in which blister-like growths of metal oxides develop in pipes as a result of the corrosion of the pipe metal. Iron oxide tubercles often develop over pits in iron or steel pipe, and can seriously restrict the flow of water.
turbidity - The amount of small particles of solid matter suspended in water as measured by the amount of scattering and absorption of light rays caused by the particles. Turbidity blocks light rays and makes the water opaque. Turbidity is measured in nephelometric turbidity units (NTU). Potable water should not exceed 0.5 NTU. Turbidity cannot be directly equated to suspended solids because white particles reflect more light than dark-colored particles and many small particles will reflect more light than an equivalent large particle.
turbulent flow (turbulence) - A type of flow characterized by cross currents and eddies, as opposed to laminar or streamlined flow. Turbulence may be caused by surface roughness or protrusions in pipes, bends and fittings, changes in channel size, or excessive flow rates; turbulence significantly increases pressure drops.