Learn about salinity and related concepts

Learn about salinity and water quality


Water quality parameters and constituents of interest

Inorganic ions and compounds commonly found in natural waters
Bicarbonate HCO3-
Sulfate SO4--
Chloride Cl-
Nitrate NO3-
Ca2+, Mg2+, Na+, K+, Fe2+
Silica Si(OH)4

With regard to landscape irrigation, the most important water quality parameters are as follows:

  • total concentration of soluble salts, also known as total dissolved solids (TDS),
  • electrical conductivity (EC),
  • concentrations of specific ions or elements that can be toxic to plants, especially sodium (Na+), chloride (Cl-), and boron (B),
  • concentrations of bicarbonate ion (HCO3-) and carbonate ion (CO32-),
  • sodium adsorption ratio (SAR),
  • pH
  • concentrations of plant nutrients, in particular, nitrogen, phosphorus, and potassium,
  • residual chlorine, potentially detrimental to the growth of plants,
  • suspended solids, which can lead to clogging of water application systems, and
  • concentrations of trace elements.

The total dissolved solids (TDS) can be measured directly; however, the procedure is time-consuming. It is common nowadays instead to estimate TDS from the water's electrical conductivity (EC). TDS, EC, and the equation relating the two are described elsewhere in this tutorial.

Usually, the main cations in irrigation water are sodium (Na+), calcium (Ca2+), and magnesium (Mg2+). The main anions typically are chloride (Cl-), sulfate (SO42-), and bicarbonate (HCO3-).

Potassium (K+) may be present, but its concentration typically is kept low by interactions with soil particles, especially clay minerals. Likewise, carbonate (CO32-) generally is not a major constituent, except under unusual circumstances. It can become a major element only when a water's pH exceeds 8.0 — a situation that is relatively uncommon for fresh waters. Boron (B) is present in most irrigation waters. Typically, in surface waters it occurs only at low concentration, whereas in groundwater, its concentration can range quite a bit higher.

Several other parameters pertain to the biological constituents of water or the effects thereof:

  • concentration of pathogens and viruses (estimated number per 100 mL of water)
  • concentration of dissolved oxygen
  • concentrations of organic chemicals that exert an oxygen demand when they decompose

These parameters are useful for studies related to health effects or environmental concerns, but are not particularly relevant for studies of salinity or the suitability of water for irrigation. Consequently, they will not be considered further here.

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