TDS - The abbreviation for "total dissolved solids".

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- A very low concentration of a substance in water. The term is sometimes used to indicate the concentration which can just be detected.

throughput volume - The amount of solution passed through an ion exchange bed before the ion exchanger is exhausted.

titration - An analytical process in which a standard solution in a calibrated vessel is added to a measured volume of sample until an endpoint, such as a color change, is reached. From the volume of the sample and the volume of standard solution used, the concentration of a specific material may be calculated.

total acidity- The total of all forms of acidity, including mineral acidity, carbon dioxide, and acid salts. Total acidity is usually determined by titration with a standard base solution to the phenolphthalein endpoint (pH 8.3). (See acidity.)

total alkalinity - The alkalinity of a water as determined by titration with standard acid solution to the methyl orange endpoint (pH approximately 4.5); sometimes abbreviated as "M" alkalinity". Total alkalinity includes many alkalinity components, such as hydroxides, carbonates, and bicarbonates. (see alkalinity.)

total cations - This is the sum of Ca + Mg _ Na + K all reported in gpg as CaCO₃. These are "positive" ions and are generally metals. Total cations should always equal total anions.

total chlorine - The total concentration of chlorine in a water, including combined and free chlorine. (See combined available chlorine, free available chlorine.)

total dissolved solids (TDS) - The weight of solids per unit volume of water which are in true solution, usually determined by the evaporation of a measured volume of filtered water, and determination of the residue weight.

total hardness - 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 - 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 105^oC in a pre-weighted dish.

toxic - Having an adverse physiological effect on humans or other desirable organisms.

trace - A very small concentration of a material, high enough to be detected but too low to be measured by standard analytical methods.

transpiration - The process in which living plants release water vapor into the atmosphere, a significant part of the hydrologic cycle.

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 - A measure of the cloudiness in water, the result of finely divided particulate matter suspended in water; usually reported in arbitrary units determined by measurements of light scattering. (See Nephelometric Turbidity Unit.)

turbulent flow - 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.