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Total dissolved solids (TDS) is a measure of the dissolved combined content of all
inorganic In chemistry, an inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds, that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as ''inorganic chemist ...
and
organic Organic may refer to: * Organic, of or relating to an organism, a living entity * Organic, of or relating to an anatomical organ Chemistry * Organic matter, matter that has come from a once-living organism, is capable of decay or is the product ...
substances present in a liquid in
molecular A molecule is a group of two or more atoms held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions which satisfy this criterion. In quantum physics, organic chemistry, and bio ...
, ionized, or micro-granular ( colloidal sol) suspended form. TDS concentrations are often reported in parts per million (ppm). Water TDS concentrations can be determined using a digital meter. Generally, the operational definition is that the solids must be small enough to survive filtration through a filter with 2-micrometer (nominal size, or smaller) pores. Total dissolved solids are normally discussed only for
freshwater Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salts and other total dissolved solids. Although the term specifically excludes seawater and brackish water, it does incl ...
systems, as
salinity Salinity () is the saltiness or amount of salt (chemistry), salt dissolved in a body of water, called saline water (see also soil salinity). It is usually measured in g/L or g/kg (grams of salt per liter/kilogram of water; the latter is dimensio ...
includes some of the ions constituting the definition of TDS. The principal application of TDS is in the study of
water quality Water quality refers to the chemical, physical, and biological characteristics of water based on the standards of its usage. It is most frequently used by reference to a set of standards against which compliance, generally achieved through tr ...
for
stream A stream is a continuous body of surface water flowing within the bed and banks of a channel. Depending on its location or certain characteristics, a stream may be referred to by a variety of local or regional names. Long large streams ...
s,
river A river is a natural flowing watercourse, usually freshwater, flowing towards an ocean, sea, lake or another river. In some cases, a river flows into the ground and becomes dry at the end of its course without reaching another body of ...
s, and
lake A lake is an area filled with water, localized in a basin, surrounded by land, and distinct from any river or other outlet that serves to feed or drain the lake. Lakes lie on land and are not part of the ocean, although, like the much large ...
s. Although TDS is not generally considered a primary
pollutant A pollutant or novel entity is a substance or energy introduced into the environment that has undesired effects, or adversely affects the usefulness of a resource. These can be both naturally forming (i.e. minerals or extracted compounds like o ...
(e.g. it is not deemed to be associated with health effects), it is used as an indication of aesthetic characteristics of
drinking water Drinking water is water that is used in drink or food preparation; potable water is water that is safe to be used as drinking water. The amount of drinking water required to maintain good health varies, and depends on physical activity level, ...
and as an aggregate indicator of the presence of a broad array of chemical contaminants. Primary sources for TDS in receiving waters are agricultural runoff and residential (urban) runoff, clay-rich mountain waters, leaching of
soil contamination Soil contamination, soil pollution, or land pollution as a part of land degradation is caused by the presence of xenobiotic (human-made) chemicals or other alteration in the natural soil environment. It is typically caused by industrial activity ...
, and point source
water pollution Water pollution (or aquatic pollution) is the contamination of water bodies, usually as a result of human activities, so that it negatively affects its uses. Water bodies include lakes, rivers, oceans, aquifers, reservoirs and groundwater. ...
discharge from industrial or
sewage treatment Sewage treatment (or domestic wastewater treatment, municipal wastewater treatment) is a type of wastewater treatment which aims to remove contaminants from sewage to produce an effluent that is suitable for discharge to the surrounding en ...
plants. The most common chemical constituents are
calcium Calcium is a chemical element with the symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar ...
,
phosphate In chemistry, a phosphate is an anion, salt, functional group or ester derived from a phosphoric acid. It most commonly means orthophosphate, a derivative of orthophosphoric acid . The phosphate or orthophosphate ion is derived from phosph ...
s,
nitrate Nitrate is a polyatomic ion with the chemical formula . Salts containing this ion are called nitrates. Nitrates are common components of fertilizers and explosives. Almost all inorganic nitrates are soluble in water. An example of an insolu ...
s,
sodium Sodium is a chemical element with the symbol Na (from Latin ''natrium'') and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 of the periodic table. Its only stable ...
,
potassium Potassium is the chemical element with the symbol K (from Neo-Latin '' kalium'') and atomic number19. Potassium is a silvery-white metal that is soft enough to be cut with a knife with little force. Potassium metal reacts rapidly with atmos ...
, and
chloride The chloride ion is the anion (negatively charged ion) Cl−. It is formed when the element chlorine (a halogen) gains an electron or when a compound such as hydrogen chloride is dissolved in water or other polar solvents. Chloride s ...
, which are found in
nutrient A nutrient is a substance used by an organism to survive, grow, and reproduce. The requirement for dietary nutrient intake applies to animals, plants, fungi, and protists. Nutrients can be incorporated into cells for metabolic purposes or excre ...
runoff, general
stormwater Stormwater, also spelled storm water, is water that originates from precipitation ( storm), including heavy rain and meltwater from hail and snow. Stormwater can soak into the soil ( infiltrate) and become groundwater, be stored on depressed l ...
runoff and runoff from snowy climates where road
de-icing Deicing is the process of removing snow, ice or frost from a surface. Anti-icing is the application of chemicals that not only deice but also remain on a surface and continue to delay the reformation of ice for a certain period of time, or prev ...
salts are applied. The chemicals may be
cation An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conven ...
s,
anion An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conve ...
s,
molecule A molecule is a group of two or more atoms held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions which satisfy this criterion. In quantum physics, organic chemistry, and b ...
s or agglomerations on the order of one thousand or fewer molecules, so long as a soluble micro- granule is formed. More exotic and harmful elements of TDS are
pesticide Pesticides are substances that are meant to control pests. This includes herbicide, insecticide, nematicide, molluscicide, piscicide, avicide, rodenticide, bactericide, insect repellent, animal repellent, microbicide, fungicide, and ...
s arising from
surface runoff Surface runoff (also known as overland flow) is the flow of water occurring on the ground surface when excess rainwater, stormwater, meltwater, or other sources, can no longer sufficiently rapidly infiltrate in the soil. This can occur when t ...
. Certain naturally occurring total dissolved solids arise from the weathering and dissolution of rocks and soils. The United States has established a secondary water quality standard of 500 mg/L to provide for palatability of drinking water. Total dissolved solids are differentiated from total suspended solids (TSS), in that the latter cannot pass through a sieve of 2 micrometers and yet are indefinitely suspended in solution. The term ''settleable solids'' refers to material of any size that will not remain suspended or dissolved in a holding tank not subject to motion, and excludes both TDS and TSS. Settleable solids may include larger particulate matter or insoluble molecules. Total dissolved solids include both volatile and non-volatile solids. Volatile solids are ones that can easily go from a solid to a liquid state. Non-volatile solids must be heated to a high temperature, typically 550 °C, in order to achieve this state change. Examples of non-volatile substances include salts and sugars.


Measurement

The two principal methods of measuring total dissolved solids are gravimetric analysis and conductivity. Gravimetric methods are the most accurate and involve evaporating the liquid
solvent A solvent (s) (from the Latin '' solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a solution. A solvent is usually a liquid but can also be a solid, a gas, or a supercritical fluid. Water is a solvent for ...
and measuring the mass of residues left. This method is generally the best, although it is time-consuming. If inorganic salts comprise the great majority of TDS, conductivity-based methods are appropriate. Electrical, or specific, conductivity of water is directly related to the concentration of dissolved ionized solids in the water. Ions from the dissolved solids in water create the ability for that water to conduct an
electric current An electric current is a stream of charged particles, such as electrons or ions, moving through an electrical conductor or space. It is measured as the net rate of flow of electric charge through a surface or into a control volume. The movi ...
, which can be measured using a conventional conductivity meter or TDS meter. When correlated with laboratory TDS measurements, conductivity provides an approximate value for the TDS
concentration In chemistry, concentration is the abundance of a constituent divided by the total volume of a mixture. Several types of mathematical description can be distinguished: '' mass concentration'', '' molar concentration'', ''number concentration'', ...
, usually to within ten-percent accuracy. The relationship of TDS and specific conductance of groundwater can be approximated by the following equation: :''TDS = keEC'' where TDS is expressed in mg/L and EC is the electrical conductivity in microsiemens per centimeter at 25 °C. The conversion factor ''ke'' varies between 0.55 and 0.8. Some TDS meters will use this electrical conductivity measurement to then infer the number of
parts per million In science and engineering, the parts-per notation is a set of pseudo-units to describe small values of miscellaneous dimensionless quantities, e.g. mole fraction or mass fraction. Since these fractions are quantity-per-quantity measures, th ...
(ppm) using the above formula; 1 ppm indicates 1 mg of dissolved solids per kg of water.


Hydrological simulation

Hydrologic transport models are used to mathematically analyze movement of TDS within river systems. The most common models address surface runoff, allowing variation in
land use Land use involves the management and modification of natural environment or wilderness into built environment such as settlements and semi-natural habitats such as arable fields, pastures, and managed woods. Land use by humans has a long ...
type,
topography Topography is the study of the forms and features of land surfaces. The topography of an area may refer to the land forms and features themselves, or a description or depiction in maps. Topography is a field of geoscience and planetary sc ...
,
soil Soil, also commonly referred to as earth or dirt, is a mixture of organic matter, minerals, gases, liquids, and organisms that together support life. Some scientific definitions distinguish ''dirt'' from ''soil'' by restricting the former ...
type, vegetative cover,
precipitation In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls under gravitational pull from clouds. The main forms of precipitation include drizzle, rain, sleet, snow, ice pellets, graupel and hail. ...
, and land management practice (e.g. the application rate of a
fertilizer A fertilizer (American English) or fertiliser (British English; see spelling differences) is any material of natural or synthetic origin that is applied to soil or to plant tissues to supply plant nutrients. Fertilizers may be distinct from ...
). Runoff models have evolved to a good degree of accuracy and permit the evaluation of alternative land management practices upon impacts to stream water quality. Basin models are used to more comprehensively evaluate total dissolved solids within a catchment basin and dynamically along various stream reaches. The DSSAM model was developed by the U.S. Environmental Protection Agency (EPA).C.M. Hogan, Marc Papineau et al. ''Development of a dynamic water quality simulation model for the Truckee River'', Earth Metrics Inc., Environmental Protection Agency Technology Series, Washington D.C. (1987) This hydrology transport model is actually based upon the pollutant-loading metric called " Total Maximum Daily Load" (TMDL), which addresses TDS and other specific chemical pollutants. The success of this model contributed to the Agency's broadened commitment to the use of the underlying TMDL protocol in its national policy for management of many river systems in the United States.


Practical implications

When measuring water treated with
water softener Water softening is the removal of calcium, magnesium, and certain other metal cations in hard water. The resulting soft water requires less soap for the same cleaning effort, as soap is not wasted bonding with calcium ions. Soft water also extend ...
s, high levels of total dissolved solids do not correlate to hard water, as water softeners do not reduce TDS; rather, they replace magnesium and calcium ions, which cause hard water, with an equal charge of sodium or potassium ions, e.g. Ca2+ ⇌ 2 Na+, leaving overall TDS unchanged or even increased. Hard water can cause scale buildup in pipes,
valve A valve is a device or natural object that regulates, directs or controls the flow of a fluid (gases, liquids, fluidized solids, or slurries) by opening, closing, or partially obstructing various passageways. Valves are technically fitting ...
s, and filters, reducing performance and adding to system maintenance costs. These effects can be seen in
aquarium An aquarium (plural: ''aquariums'' or ''aquaria'') is a vivarium of any size having at least one transparent side in which aquatic plants or animals are kept and displayed. Fishkeepers use aquaria to keep fish, invertebrates, amphibians, aq ...
s,
spas Spas or SPAS may refer to: * Spa, a therapeutic water treatment Geography * Spas, Russia, several rural localities in Russia * Spas, Lviv Raion, Lviv Oblast, a village in Lviv Raion in Lviv Oblast, Ukraine * Spas, Sambir Raion, Lviv Oblast, a vil ...
,
swimming pool A swimming pool, swimming bath, wading pool, paddling pool, or simply pool, is a structure designed to hold water to enable Human swimming, swimming or other leisure activities. Pools can be built into the ground (in-ground pools) or built ...
s, and
reverse osmosis Reverse osmosis (RO) is a water purification process that uses a partially permeable membrane to separate ions, unwanted molecules and larger particles from drinking water. In reverse osmosis, an applied pressure is used to overcome osmotic ...
water treatment Water treatment is any process that improves the quality of water to make it appropriate for a specific end-use. The end use may be drinking, industrial water supply, irrigation, river flow maintenance, water recreation or many other uses, inc ...
systems. Typically, in these applications, total dissolved solids are tested frequently, and filtration membranes are checked in order to prevent adverse effects. In the case of
hydroponics Hydroponics is a type of horticulture and a subset of hydroculture which involves growing plants, usually crops or medicinal plants, without soil, by using water-based mineral nutrient solutions in aqueous solvents. Terrestrial or aquatic plant ...
and
aquaculture Aquaculture (less commonly spelled aquiculture), also known as aquafarming, is the controlled cultivation ("farming") of aquatic organisms such as fish, crustaceans, mollusks, algae and other organisms of value such as aquatic plants (e.g. lot ...
, TDS is often monitored in order to create a water quality environment favorable for
organism In biology, an organism () is any living system that functions as an individual entity. All organisms are composed of cells ( cell theory). Organisms are classified by taxonomy into groups such as multicellular animals, plants, and fu ...
productivity. For freshwater
oyster Oyster is the common name for a number of different families of salt-water bivalve molluscs that live in marine or brackish habitats. In some species, the valves are highly calcified, and many are somewhat irregular in shape. Many, but not ...
s,
trout Trout are species of freshwater fish belonging to the genera '' Oncorhynchus'', '' Salmo'' and '' Salvelinus'', all of the subfamily Salmoninae of the family Salmonidae. The word ''trout'' is also used as part of the name of some non-salm ...
s, and other high value
seafood Seafood is any form of sea life regarded as food by humans, prominently including fish and shellfish. Shellfish include various species of molluscs (e.g. bivalve molluscs such as clams, oysters and mussels, and cephalopods such as octopus an ...
, highest productivity and economic returns are achieved by mimicking the TDS and pH levels of each
species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriat ...
' native environment. For hydroponic uses, total dissolved solids is considered one of the best indices of nutrient availability for the aquatic plants being grown. Because the threshold of acceptable
aesthetic Aesthetics, or esthetics, is a branch of philosophy that deals with the nature of beauty and taste, as well as the philosophy of art (its own area of philosophy that comes out of aesthetics). It examines aesthetic values, often expressed t ...
criteria for human drinking water is 500 mg/L, there is no general concern for
odor An odor (American English) or odour (Commonwealth English; see spelling differences) is caused by one or more volatilized chemical compounds that are generally found in low concentrations that humans and animals can perceive via their sense ...
, taste, and
color Color (American English) or colour (British English) is the visual perceptual property deriving from the spectrum of light interacting with the photoreceptor cells of the eyes. Color categories and physical specifications of color are associ ...
at a level much lower than is required for harm. A number of studies have been conducted and indicate various species' reactions range from intolerance to outright toxicity due to elevated TDS. The numerical results must be interpreted cautiously, as true toxicity outcomes will relate to specific chemical constituents. Nevertheless, some numerical information is a useful guide to the nature of risks in exposing aquatic organisms or terrestrial animals to high TDS levels. Most aquatic ecosystems involving mixed fish fauna can tolerate TDS levels of 1000 mg/L. The
fathead minnow Fathead minnow (''Pimephales promelas''), also known as fathead or tuffy, is a species of temperate freshwater fish belonging to the genus '' Pimephales'' of the cyprinid family. The natural geographic range extends throughout much of North A ...
(''Pimephales promelas''), for example, realizes an concentration of 5600 ppm based upon a 96-hour exposure. LD50 is the concentration required to produce a lethal effect on 50 percent of the exposed
population Population typically refers to the number of people in a single area, whether it be a city or town, region, country, continent, or the world. Governments typically quantify the size of the resident population within their jurisdiction usi ...
. ''
Daphnia magna ''Daphnia magna'' is a small planktonic crustacean (adult length 1.5–5.0 mm) that belongs to the subclass Phyllopoda. Description ''D. magna'' is a typical water flea of the genus ''Daphnia''. The females reach up to 5 mm in size, ...
'', a good example of a primary member of the
food chain A food chain is a linear network of links in a food web starting from producer organisms (such as grass or algae which produce their own food via photosynthesis) and ending at an apex predator species (like grizzly bears or killer whales), de ...
, is a small
plankton Plankton are the diverse collection of organisms found in water (or air) that are unable to propel themselves against a current (or wind). The individual organisms constituting plankton are called plankters. In the ocean, they provide a cruc ...
ic
crustacean Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapoda, decapods, ostracoda, seed shrimp, branchiopoda, branchiopods, argulidae, fish lice, krill, remipedes, isopoda, isopods, barnacles, copepods, ...
, about 0.5 mm in length, having an LD50 of about 10,000 ppm TDS for a 96-hour exposure.
Spawning Spawn is the eggs and sperm released or deposited into water by aquatic animals. As a verb, ''to spawn'' refers to the process of releasing the eggs and sperm, and the act of both sexes is called spawning. Most aquatic animals, except for aquat ...
fish Fish are Aquatic animal, aquatic, craniate, gill-bearing animals that lack Limb (anatomy), limbs with Digit (anatomy), digits. Included in this definition are the living hagfish, lampreys, and Chondrichthyes, cartilaginous and bony fish as we ...
es and juveniles appear to be more sensitive to high TDS levels. For example, it was found that concentrations of 350 mg/L TDS reduced spawning of
Striped bass The striped bass (''Morone saxatilis''), also called the Atlantic striped bass, striper, linesider, rock, or rockfish, is an anadromous perciform fish of the family Moronidae found primarily along the Atlantic coast of North America. It has ...
(''Morone saxatilis'') in the
San Francisco Bay San Francisco Bay is a large tidal estuary in the U.S. state of California, and gives its name to the San Francisco Bay Area. It is dominated by the big cities of San Francisco, San Jose, and Oakland. San Francisco Bay drains water f ...
-Delta region, and that concentrations below 200 mg/L promoted even healthier spawning conditions. In the
Truckee River The Truckee River is a river in the U.S. states of California and Nevada. The river flows northeasterly and is long.U.S. Geological Survey. National Hydrography Dataset high-resolution flowline dataThe National Map accessed October 20, 2012 Th ...
, EPA found that juvenile Lahontan cutthroat trout were subject to higher mortality when exposed to
thermal pollution Thermal pollution, sometimes called "thermal enrichment", is the degradation of water quality by any process that changes ambient water temperature. Thermal pollution is the rise or fall in the temperature of a natural body of water caused by hum ...
stress combined with high total dissolved solids concentrations. For terrestrial animals, poultry typically possess a safe upper limit of TDS exposure of approximately 2900 mg/L, whereas dairy cattle are measured to have a safe upper limit of about 7100 mg/L. Research has shown that exposure to TDS is compounded in toxicity when other stressors are present, such as abnormal pH, high
turbidity Turbidity is the cloudiness or haziness of a fluid caused by large numbers of individual particles that are generally invisible to the naked eye, similar to smoke in air. The measurement of turbidity is a key test of water quality. Fluids ...
, or reduced
dissolved oxygen Oxygen saturation (symbol SO2) is a relative measure of the concentration of oxygen that is dissolved or carried in a given medium as a proportion of the maximal concentration that can be dissolved in that medium at the given temperature. It ca ...
with the latter stressor acting only in the case of Animalia. In countries with often-unsafe/unclean tap water supplies, the TDS of drinking water is often checked by technicians to gauge how effectively their RO/Water Filtration devices are working. While TDS readings will not give an answer as to the amount of microorganisms present in a sample of water, they can get a good idea as to the efficiency of the filter by how much TDS is present.


Water classification

Water can be classified by the level of total dissolved solids (TDS) in the water: *
Fresh water Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salts and other total dissolved solids. Although the term specifically excludes seawater and brackish water, it does incl ...
: TDS is less than 1,000 ppm *
Brackish water Brackish water, sometimes termed brack water, is water occurring in a natural environment that has more salinity than freshwater, but not as much as seawater. It may result from mixing seawater (salt water) and fresh water together, as in estuari ...
: TDS = 1,000 to 10,000 ppm *
Saline water Saline water (more commonly known as salt water) is water that contains a high concentration of dissolved salts (mainly sodium chloride). On the United States Geological Survey (USGS) salinity scale, saline water is saltier than brackish water ...
: TDS = 10,000 to 35,000 ppm * Hypersaline: TDS greater than 35,000 ppm Drinking water generally has a TDS below 500 ppm. Higher TDS Fresh Water is drinkable but taste may be objectionable.


See also

*
Acid rain Acid rain is rain or any other form of precipitation that is unusually acidic, meaning that it has elevated levels of hydrogen ions (low pH). Most water, including drinking water, has a neutral pH that exists between 6.5 and 8.5, but ac ...
*
Surface runoff Surface runoff (also known as overland flow) is the flow of water occurring on the ground surface when excess rainwater, stormwater, meltwater, or other sources, can no longer sufficiently rapidly infiltrate in the soil. This can occur when t ...
*Regarding meters: **
EC meter An electrical conductivity meter (EC meter) measures the electrical conductivity in a solution. It has multiple applications in research and engineering, with common usage in hydroponics, aquaculture, aquaponics, and freshwater systems to moni ...
**
pH meter A pH meter is a scientific instrument that measures the hydrogen-ion activity in water-based solutions, indicating its acidity or alkalinity expressed as pH. The pH meter measures the difference in electrical potential between a pH elect ...
** Salinometer


References


External links

* {{Chemical solutions Environmental chemistry Homogeneous chemical mixtures Water pollution Water quality indicators