Difference Between TDS and Salinity

calendarMar 14, 2023 · 4 min read  ·
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The key difference between TDS and salinity is that TDS is the measurement of all types of solid compounds in a given liquid sample whereas salinity is the measurement of the amount of salt that is dissolved in a given liquid sample.

Often, people use the terms TDS and salinity interchangeably though they are two different terms. The term TDS stands for total dissolved solids while salinity refers to the dissolved salt amount in water.

CONTENTS

1. Overview and Key Difference
2. What is TDS
3. What is Salinity
4. Side by Side Comparison – TDS vs Salinity in Tabular Form
5. Summary

What is TDS?

TDS is total dissolved solids. It is a measure of the dissolved combined content of all inorganic and organic substances in a liquid. The liquid can exist in molecular, ionized, or in the micro granular suspended form. The unit of measurement of this parameter is usually “part per million (ppm)”. We can easily determine the TDS level of water using a digital meter.

The solid particles in the given liquid sample must be small enough to go through the pore of a filter having the pore size 2 micrometre. The most important application of TDS parameter is the study of water quality for streams, rivers, and lakes. We can use this parameter as an indication of aesthetic qualities of drinking water and as an aggregate indicator though it is not generally considered as a primary pollutant that causes any health effect. There are several different primary sources of TDS including,

  • Agricultural runoff
  • Residential runoff
  • Clay-rich mountain waters
  • Leaching of soil contamination
  • Point source water pollution from industrial sites
  • Sewage treatment plants

    • The chemical components we can easily find in liquids like calcium, phosphate, nitrates, sodium, potassium, and chloride can cause TDS levels. We can find these chemical components mostly in nutrient runoff, general stormwater runoff, and runoff from snowy climates where deicing agents are applied.

    The form of dissolved chemical substances in liquids with a high TDS level can be cations, anions, molecules or agglomerates. The toxic chemical components that can cause harmful health effects due to high TDS levels in water are pesticides that arise from surface runoff. Some naturally occurring total dissolved solids come from the weathering and dissolution of rocks and soils.

    What is Salinity?

    Salinity is the measurement of the amount of salt dissolved in a water body. We can measure this value by dividing the gram amount of salt in the given sample from kilogram amount of seawater. Salinity is an important parameter in determining many aspects regarding the chemistry of natural water and the biological processes within the water body. Moreover, it is a thermodynamic state variable that governs physical characteristics such as the density and heat capacity of the water.

    Difference Between TDS and Salinity

    We can classify water bodies according to the salinity level of water. E.g. hyperhaline, metahaline, mixoeuhaline, polyhaline, mesohaline, and oligohaline water bodies. Furthermore, the salinity of the water has importance as an ecological factor that influences the kinds of plants that can grow either in a water body or even on land that is fed by water.

    What is the Difference Between TDS and Salinity?

    The term TDS stands for total dissolved solids while salinity refers to the dissolved salt amount in water. The key difference between TDS and salinity is that TDS is the measurement of all types of solid compounds in a given water sample whereas salinity is the measure of the amount of salt that is dissolved in a given water sample.

    Below is a summary tabulation of the difference between TDS and salinity.

    Difference Between TDS and Salinity in Tabular Form

    Summary – TDS vs Salinity

    TDS stands for total dissolved solids while salinity refers to the dissolved salt amount in water. The key difference between TDS and salinity is that TDS is the measurement of all types of solid compounds in a given water sample whereas salinity is the measure of the amount of salt that is dissolved in a given water sample.

    Reference:

    1. “Understanding Salinity.” Western Australian Government, Department of Water, Available here.

    Image Courtesy:

    1. “Water salinity diagram” By Peter Summerlin – Own work (CC BY-SA 3.0) via Commons Wikimedia

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