{"id":1966,"date":"2017-04-03T07:58:36","date_gmt":"2017-04-03T07:58:36","guid":{"rendered":"http:\/\/www.experimentoscientificos.es\/?page_id=1966"},"modified":"2018-02-21T16:07:16","modified_gmt":"2018-02-21T16:07:16","slug":"conductividad-del-agua","status":"publish","type":"page","link":"https:\/\/www.experimentoscientificos.es\/en\/conductividad\/conductividad-del-agua\/","title":{"rendered":"Water Conductivity"},"content":{"rendered":"

WHAT IS THE CONDUCTIVITY OF WATER<\/h2>\n

Conductivity is the ability of a material to allow electric current to pass through it. To know the conductivity of water, it is necessary to know what type of water we are talking about. Pure water, H2O<\/strong>does not conduct electricity. However, practically all water with which we are in contact (tap, mineral, rain, sea...) is not pure water, but water with a solution of salts in different concentrations. The salts in the water have the capacity to transport electrical energy. Since all the water with which we are in contact has dissolved salts, the water with which we are in contact has a different concentration of salts. if it conducts electricity<\/strong>. Given this direct relationship between the salinity<\/a> and conductivity, conductivity is used to measure the salinity of water.<\/p>\n

The value given for the conductivity of a solution is referenced to 25 \u00b0C. The units of measurement for conductivity are in unit of resistance\/unit of length. The most commonly used are dS\/m (deciSiemens per metre), mmhos\/cm (millimhos per centimetre) and mS\/m (milliSiemens per metre).<\/p>\n

\"Conductividad<\/p>\n

HOW TO MEASURE CONDUCTIVITY<\/h2>\n

The conductivity of water is measured with an EC conductivity meter. The conductivity in water is measured using an amperometric (measuring current) or potentiometric (measuring power) system. The higher the current flow or the more power is generated, the higher the conductivity. siemens per centimetre (s\/cm) or millisiemens per centimetre<\/strong> (ms\/cm).<\/p>\n

Once we have the conductivity value it is possible to convert it to a salinity value by multiplying it by a factor and it will give you the salinity in mg\/L. This factor depends on the type of water you are measuring, but as a reference value you can take 0.6 or 0.7 for this factor, in the next section you can see examples of conversions for different types of water.<\/p>\n

It is precisely these measuring devices, known as dissolved solids meters, TDS<\/strong> which gives you the dissolved solids value directly. This device works by conductivity and applies the factor to give you the dissolved solids value in ppm.<\/p>\n

TDS<\/h3>\n

TDS<\/strong> Total Dissolved Solids (TDS) are the amount of salts or solids in a given solution. They are measured in ppm (parts per million).<\/p>\n

The theoretical and intuitive way to measure TDS would be to take a 1L solution and evaporate all the water. Weigh the resulting solids, and we would get the resulting solids (in mg). For example if the remainder weighed 400mg we would have a TDS of 400ppm.<\/p>\n

This system for measuring solids would be quite cumbersome. As we have already mentioned, the conductivity of a solution is proportional to its salt content, which is why the EC conductivity is used to measure TDS. This TDS meter<\/a> is simple, fast and very economical and has a correction factor between EC conductivity and dissolved solids.<\/p>\n

EC<\/h3>\n

EC, or Electrical Conductivity. By measuring conductivity we can find out the salt content of a solution, since the more salts it contains, the better it will conduct electricity.<\/p>\n

Conductivity is measured in siemens per centimetre (s\/cm) or millisiemens per centimetre<\/strong> (ms\/cm). Since these measurements do not tell us anything, the TDS meter converts conductivity<\/strong> \u00a0a ppm<\/strong> using a conversion factor<\/strong> (i.e. by multiplying it by a specific number). The problem with this conversion is that the factor depends on the composition of the salts.<\/p>\n

These factors also change depending on the manufacturer, for example in the USA 1 ms\/cm is equivalent to 500 ppm, in Europe 1ms\/cm is 640 ppm and in Australia 1 ms\/cm is 700 ppm. It can therefore be difficult to compare ppm values from one person to another, as they may be using different conversion factors. There is a partial solution to this, if your meter gives you EC and PPM you can calculate the conversion factor:<\/p>\n

Conversion factor = ppm\/ec<\/strong><\/p>\n

[Important, EC must be in \u00b5s and not in ms. To do this multiply ms by 1000]<\/p>\n

<\/h3>\n

Conductivity measurements<\/span><\/p>\n

The salt content in water is what gives it the ability to conduct electricity. The more salts are dissolved in the water, the more the water will conduct electricity. Each case is different, but an order of magnitude of conductivity values in water would be as follows:<\/p>\n

Pure water:<\/strong> 0.055 \u00b5S\/cm
\nDistilled water:<\/strong> 0.5 \u00b5S\/cm
\nMountain water:<\/strong> 1.0 \u00b5S\/cm
\nWater for domestic use:<\/strong> 500 to 800 \u00b5S\/cm
\nMax. for drinking water:<\/strong> 10055 \u00b5S\/cm
\nSeawater:<\/strong> 52 mS\/cm<\/p>\n

Once we have the conductivity we can obtain the salinity, multiplying by a factor of 0.6 or 0.7 to obtain the salinity value in mg\/L. In this case the salinity would be:<\/p>\n

Pure water:<\/strong> 0,033-0,0385 mg\/L
\nDistilled water:<\/strong> 0,3 - 0,385 mg\/L
\nMountain water:<\/strong> 0.6 - 0.7 mg\/L
\nWater for domestic use:<\/strong> 300 - 560 mg\/L
\nMax. for drinking water:<\/strong>\u00a06033 - 7033 mg\/L
\nSeawater:<\/strong> 31,2 - 36,4 g\/L<\/p>\n

Density is a factor directly proportional to salinity, and therefore to conductivity. It is not only proportional to salinity but also depends on temperature. The lower the temperature, the higher the density (that is why cold water is found more at the bottom) and this is the reason for the climate-regulating ocean currents.<\/p>\n

When we talk about density we take as a reference 1atm and 4\u00baC. Under these conditions the density of pure water is 1000Kg\/m3. The density depends not only on salinity, but also on pressure and temperature. Especially in surface water we will notice the effect of temperature, being at about 20\u00baC the density of pure water 996Kg\/m3. At the surface of seawater, where the salinity is 31.2-36g\/L, the density is 1025-1027Kg\/m3.<\/p>\n

TO MEASURE SALINITY AND DENSITY FROM CONDUCTIVITY AND DISSOLVED SOLIDS<\/h2>\n

Let's see how salinity values are measured from the dissolved solids measurement. This measuring instrument is actually measuring the conductivity of the water and giving us the ppm in salinity with a factor of 0.6-0.7.<\/p>\n

    \n
  1. The water sample is taken<\/li>\n
  2. The TDS measuring device<\/a> in the water to be measured.<\/li>\n
  3. You read the value it gives you. Let's take as an example a tap water with a value of 220.<\/li>\n
  4. We interpret the reading:\n
      \n
    1. The units of measurement are mg\/L. That is 220mg\/L. This means a salinity of 2,2%<\/strong><\/li>\n
    2. This value also approximates the density, or at least its order of magnitude. The density of a liquid depends on its temperature and pressure. For example, pure water has a density of 1000Kg\/m3 at 4\u00baC and 1\u00baatm. At 30\u00ba this density decreases to 998Kg\/m3.<\/li>\n<\/ol>\n<\/li>\n<\/ol>\n