# Temperature Measurements  ## What is water temperature? On a conceptual level, water temperature can be very simple: it is a value that indicates how hot or cold a body, object or, in this case, liquid is. However, water, especially in large masses, can present enormous variations between different parts: on the surface vs. at different depths, or on the shoreline vs. further offshore. ## Why is it important? Temperature is a very important factor, because it conditions all other water factors. In addition, it is an ecological factor of considerable importance, and it has an influence on the types of organisms that can live in water: normally, the higher the temperature, the greater the biological activity. It has a direct impact on dissolved oxygen (inversely - the higher the temperature, the lower the dissolved oxygen under equal conditions), in addition to conditioning the rate at which chemical reactions occur in water. It has an impact on the dissolution of salts and metals and therefore has an impact on electrical conductivity. !!! seawater "In the sea" It is related to the salinity of currents in the ocean, and in general, changes in temperature in the oceans are due to exchanges with the atmosphere. ## How is temperature measured? Whenever possible, take readings using the temperature probe in situ, submerging it directly into the water. Try not to affect the measurements, taking the thermometer as far away from the metal part as possible to avoid heating it up. If the thermometer needs time to stabilize, take several measurements and write them down, along with the time, or take the last measurement (and only that) as valid. If it is not possible to introduce the sensor directly into into the water, and you need to take a sample, stabilize the sampling vessel before measuring (submerging it in water to warm/cool it to the same temperature as the water). ## Reference levels What is a _good_ water temperature depends on the species and the ecosystem, but warmer water holds less [dissolved oxygen](https://docs.smartcitizen.me/knowledge/soil-water/DO.md) and speeds up biological activity, so high temperatures are generally a stress factor. Some references: | Reference | Value | |:- |:- | | Cold water fish (trout, salmon) | Prefer temperatures below ~15 ºC, stressed above ~20 ºC | | EU salmonid waters [^1] | Maximum 21.5 ºC | | EU cyprinid waters (carp, etc.) [^1] | Maximum 28 ºC | | Legionella in water systems [^2] | Grows between 25 and 45 ºC. Hot water should be stored at 60 ºC or more, and cold water kept below 25 ºC (ideally below 20 ºC) | As with other parameters, sudden changes in temperature (for instance, near the discharge of cooling water from an industry) can be more harmful than the absolute value. ## Supported sensors - [Atlas Temperature](https://docs.smartcitizen.me/knowledge/soil-water/temperature/Atlas_Temperature.md) (Field | watersoil; Metric | temperature; Connection | external): An encapsulated resistive sensor (RTD, resistance temperature detector). ## References [^1]: Directive 2006/44/EC of the European Parliament and of the Council of 6 September 2006 on the quality of fresh waters needing protection or improvement in order to support fish life (repealed in 2013 by the Water Framework Directive, but still a common reference). https://eur-lex.europa.eu/eli/dir/2006/44/oj. [^2]: World Health Organization. “Legionella and the Prevention of Legionellosis.” Geneva: World Health Organization, 2007. https://www.who.int/publications/i/item/9241562978.