Hydrochemical diagram for water models. The different softwares that are used for working with water models use different hydrochemical diagrams to correctly identify them. The graphic representation of the hydrochemical data constitutes a very efficient work tool in the interpretation of the properties of a water , as well as for making comparisons or correlations. It also allows you to easily see the behavior and evolution of water in a given territory and over time.
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- 1 Graphics
- 1 Piper diagrams
- 2 Schoeller diagrams
- 3 Collins diagrams
- 4 Defrancesco diagrams
- 5 Stiff diagrams
- 2 Sources
Hill and Piper triangular diagrams allow large numbers of samples to be plotted on a single graph. In these, the anion and cation triangles occupy the lower left and right angles with their bases aligned. The central part of the diagram has a rhombus shape and the points of each of the triangles are projected onto it by means of a line parallel to the upper edge of the rhombus . The intersection of these two lines represents the composition of the water with respect to a certain grouping of anions and cations.
To interpret the diagram in more detail, it must be considered that for its construction it is necessary that the ions be reduced to a percentage of milliequivalents per liter (meq / l). 100% of a cation or anion corresponds to each vertex of a triangle. 
The Schoeller or Vertical Column Diagrams represent the value in milliequivalents per liter (meq / l) of different anions, cations or a sum of them, using a logarithmic scale, and joining the points by means of a sequence of lines. This type of column diagram is also known as Schoeller – Berkaloff diagrams .
Although the logarithmic scale is not appropriate to observe small differences in the concentration of each ion between different Water Samples , it is useful to represent low and high salinity waters on the same diagram, and to observe the relationship between ions associated with the inclination of the lines.
The Collins or Column Diagrams represent the concentration of anions (on the right) and cations (on the left) in two attached columns.
The concentration value is expressed in milliequivalents per liter (meq / l), so that the height of both columns are theoretically equal. In practice, slight differences can be found due to analytical errors, or because they do not represent some ion that is in higher concentrations than normal.
It is a type of circular diagram in which the macro and micro-constituent components are represented on a logarithmic scale and the composition of the sample studied and that of the chosen water standard are represented on the same graph.
The main advantage of this diagram is that you can represent as many axes as you want. Each axis represents a chemical compound and where the graph cuts the axis represents the value of said compound for the water sample that is being analyzed.
In Stiff or Polygonal Diagrams, the concentration of anions (to the right) and cations (to the left) are represented on a logarithmic scale in parallel rays, joining the ends generating a polygon. On each ray a single ion is taken.
The shape of the resulting figures gives an idea of the type of water, lends itself to comparisons, and is easily demonstrative when inserted into hydrochemical maps. The concentration value is expressed in milliequivalents per liter (meq / l).
To construct this type of graph, the values in mg / l corresponding to the anions and cations given by the chemical analysis carried out on the sample in the laboratory are taken. To find the milli-equivalents (meq) each of the compound’s values is divided by multiplying the compound’s atomic weight by its valence, the following table shows the atomic weights of the compounds required to perform the Stiff diagram .