3 Main Water Quality Parameters Explained

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There are three main water quality parameters to measure the quality of water: physical, chemical, and biological. Physical water quality parameters include eight principle indicators: electrical conductivity, salinity, total dissolved solids, turbidity, temperature, color, and taste and odor. Chemical water parameters include pH, acidity, alkalinity, hardness, chlorine, and dissolved oxygen. The final water quality is biological, which includes bacteria, algae, nutrients, and viruses. 

Whether water is used in industrial processes or used in municipal (tap water) supplies, certain water quality parameters must be measured. For instance, the Environmental Protection Act (EPA) has set legal limits which applications must follow. The EPA states that municipal water must eradicate at least 90 different contaminants to be considered safe. 

But, water quality is not only measured by the total number of contaminants. The main water quality parameters are split into three categories: physical, chemical, and biological. 

Physical Parameters

Physical water quality parameters are observed as a result of physical changes in the water. 

Electrical Conductivity (EC)

Conductivity is a core physical water parameter. Electrical conductivity (EC) refers to the ability of water to conduct an electrical current in water over a certain distance, usually measured in Siemens (S) per distance. The power for water to conduct electricity comes from the concentration of ions within the water.

Ion content originates from dissolved solids and inorganic materials (carbonate compounds, chlorides, and sulfides). The conductance level also depends on the ion’s potential to bind with water. When the ion concentration in the water increases, the EC increases

Additionally, the conductivity of water depends on the water source. Sources of water include groundwater, municipal wastewater, rainfall, and discharge from agricultural systems. 

Electrical conductivity is essential to measure when assessing the quality of water because it can detect the level of contaminated water. Water that has a high EC has a greater amount of contaminants, whereas water that has good water quality such as drinking water has fewer contaminants, and therefore cannot conduct electricity.

The easiest way to measure EC in water is with a conductivity meter. A voltage is applied between two electrodes inside the EC probe once inserted into the water. The resistance of the water (or contaminant material) causes a drop in the voltage, which is then used to calculate the conductivity level. 

The typical conductivity ranges in different bodies of water are listed below:

  • Distilled Water: 0.5-3 
  • Tap Water: 50-800 
  • Potable Water: 30-1,500 
  • Freshwater Streams: 100-2,000 
  • Industrial Wastewater: 10,000
  • Seawater: 55,000

Salinity

Salinity refers to the salt content in water. As dissolved ions increase conductivity along with salinity, the two water parameters are measured together. The main salt ion in water that increases salinity is sodium chloride. However, other salt ions such as sodium, carbonate, chloride, and sulfate can also increase the salinity in water.

Excessive amounts of dissolved salts in water can cause numerous issues. The main issues are within drinking water and agricultural applications and aquatic ecosystem health. When salinity levels are high, corrosion of industrial machinery and infrastructure occurs. Environments with elevated dissolved salts can also pose a threat to salt-resistance species, altering the biodiversity in that area, and in severe cases, altering aquatic ecosystem structures. 

Salinity is measured in percentage (%) or parts per thousand (ppt). The best way to measure the salinity of the water is with a conductivity meter, refractometer, or hydrometer. 

Salinity Values & Applications:

  • Freshwater: <0.05% / <0.5 ppt – Drinking water and all irrigation
  • Brackish Water: 0.1-0.2% / 1-2 ppt – Irrigation for some crops
  • Saline Water: 0.2-1.0% / 2-10 ppt – Livestock
  • Very Saline Water: 1.0-3.5% / 10-35 ppt – Saline groundwater & some livestock
  • Seawater: >3.5% / >35 ppt – Mining & industrial uses

Total Dissolved Solids (TDS)

Total dissolved solids (TDS) enter the water from sewage, agricultural runoff, industrial wastewater, or the use of water treatment chemicals. The more TDS that are suspended or in suspension in water, the higher the water’s conductivity.

However, high TDS levels do not necessarily mean the water is harmful. Some water bodies may have a high amount of TDS, but the water may naturally have a high mineral content. The EPA suggests that water with a higher TDS level than 500 ppm is considered too high, and water that contains more than 1,000 ppm of TDS is considered unsafe, and therefore should not be consumed.

Even though a TDS meter is the easiest way to measure TDS levels in the water, the process is slightly more challenging as it does not tell you 

what types of TDS are present in the water. Therefore, the only true method of measuring TDS is with a home water test kit or sending a water sample for lab analysis. 

To establish what total dissolved solids are in the water, the water is evaporated and weighed. This allows you to determine the amount of organic material in the water. Yet, despite this being the most reliable and accurate method, it is the most costly. 

TDS is measured as a volume of water. The units used are milligrams per liter (mg/L) or parts per million (ppm).

Total Dissolved Solids water quality Classifications:

  • Freshwater: <1,500 mg/L 
  • Brackish Water: 1,500 – 5,000 mg/L 
  • Seawater: >5,000 mg/L 

Turbidity

Turbidity refers to the haziness of water. High turbid conditions are caused by suspended solids or tiny particles; when the concentration of total suspended solids (TSS) and TDS in the water increase, the turbidity also increases.

This is why a turbidity sensor is required in a wide range of industries and applications. For example, analyzing the cloudiness of beverages such as wine and beer and measuring the quality of water in wastewater systems, aquatic environments, and drinking water supplies. 

Turbidity levels typically increase when higher concentrations of clay, silt, and organic matter are dissolved or suspended in the water. Turbid water doesn’t just cause drinking water to go cloudy, it is also an important indicator of suspended sediments in water, the presence of pathogens, bacteria, and other contaminants.

High turbidity is linked to the following issues:

  • High treatment costs
  • Increase in the particulate matter – linked to damaged gills and inhibited growth in fish
  • Turbid water can absorb heavy metals more readily
  • Low DO levels

A nephelometer (turbidity sensor/meter) is used to measure how much light can pass through the water, measured in Nephelometric Turbidity Units (NTU) or Formazin Turbidity Units (FTU).

Old-school methods such as a Secchi disk can also be used. Oceanographers commonly use these to measure the turbidity out at sea. However, the best way to obtain high-class accuracy turbidity results is with a turbidity meter. Whichever turbidity testing method you use, the different units have been designed to standardize turbidity results.

Turbidity Levels For Drinking Water Supplies:

  • Developing Countries: <5 NTU 
  • Developed Countries: <1 NTU

Temperature

Temperature measures the kinetic energy of molecules in the water, measured in degrees Fahrenheit or Celsius. Temperature is one of the most essential parameters of water quality, as it influences biological activity and growth in water, plus it has a direct effect on the water chemistry, influencing the other main water quality parameters. 

For example, temperature affects the following other water quality parameters:

A temperature sensor is the easiest way to monitor the temperature. Temperature sensors are devices used in our everyday lives to measure the temperature in a wide range of industries and applications.

Temperature sensors provide readable measurements from electrical signals inside the temperature sensor. When a temperature change is detected, an electrical voltage or resistance is generated across the diode terminals inside the temperature probe

Color

Water that is used in the home should appear colorless. If tap water is blue or green, it is an indication of foreign substances such as microscopic organisms and particles. Decaying organic matter can also change the color of water, and this is commonly seen in stagnant pools of water like swamps.

Inorganic materials like soil and rocks can also change the water’s color. While inorganic materials can change color, they do not change the water’s taste. 

The good news is, testing the color of the water is easy, as it can be done with the naked eye. All that is needed is a series of slides or tubes to compare a water sample. There are many color card tests available for both home use and industrial applications. For high-accuracy color measurements, a tintometer (a type of color sensor) is used.

Color is typically measured in true color units (TCU), where 1 TCU is equal to the color produced by 1 mg per liter of platinum in the form of chloroplatinate ions. For drinking water supplies, the EPA standard recommends that all potable water has a color less than 15 TCU. Color is graded from 0 to 70 TCU, where pure water is almost colorless. 

Taste & Odor

The last physical water quality parameters are taste and odor. They go hand in hand, as usually when the taste of water changes, an odor is produced. This is typically from a foreign substance in the water. These are usually organic materials and inorganic compounds.

Changes in taste and odor can originate from organic materials, inorganic compounds, biological sources (aquatic microorganisms), chlorination and other water treatment issues, and microbial activity 

Typical classifications for odor:

  • A: No odor
  • B: Sulphide 
  • C: Chlorine
  • D: Earthy
  • E: Fruity
  • F: Fuel
  • G: Milky
  • H: Oily
  • I: Soapy
  • J: Fishy

Typical classifications for taste:

  • A: No taste
  • B: Sweet
  • C: Salty
  • D: Sour
  • E: Bitter

Chemical Parameters

Chemical water quality parameters assess the chemical characteristics of the water. 

pH

One of the most important chemical water quality parameters is pH, and it should always be the first measurement when assessing the quality of water. 

Elevated pH levels can lead to bitter-tasting water. High pH also causes water pipes, and other industrial appliances to become encrusted with deposits, corroding materials, and therefore, increasing toxicity levels in the water.

Increases in pH are also an issue for swimming pools and other applications that require chlorine as a disinfectant, as high pH decreases the effectiveness of chemicals. 

There are many ways to measure the pH of water. The simplest way is with a pH paper test kit. However, we always recommend a pH sensor with a pH probe for high accuracy and reliable results. A pH sensor is also the quickest way to see if water is acidic or alkaline. The pH probe detects the potential of hydrogen (pH), which has a usual range from 0-14. Readings greater than 7.0 is alkaline or a base, anything lower than 7.0 is acidic, and 7.0 is neutral. Drinking water has a pH range of 6.5 to 8.5.

Measuring pH tells us how much hydrogen is in water. For example, water that has a higher concentration of hydrogen ions is acidic, while basic water contains very little.

Using pH probes when measuring pH is important for a wide range of industries, which is why there are different pH sensors for different applications.

It is essential to frequently calibrate a pH meter, so the measurements are accurate. Over time, pH sensors can drift from their original calibrated settings. When calibration no longer fixes pH testing issues, it may be time to replace the pH probe

Acidity 

Acidity measures the level of acid in the water, measured by a pH probe/sensor. Acidic water is caused by dissolved inorganic acids, carbon dioxide, and hydrolytic salts. Acidic water can affect biological activity in water and increase corrosion from chemical reactions.

Alkalinity

Acidity indicates how well water can neutralize acids, measured using a pH sensor. Alkalinity is important for measuring water quality, as it determines how much soda ash is need to be added to neutralize the water. 

Water becomes alkaline when bicarbonate, hydroxide, and carbonate ions dissolve in water. Water that has a very high alkalinity level indicates contamination. 

Water Hardness

Water hardness refers to the mineral content of water. If water is considered hard, calcium or magnesium are likely the cause. Naturally, groundwater has a greater water hardness than surface water because groundwater is more exposed to minerals and ions. 

If hard water is left untreated, it can scale pipe systems and make it difficult to bathe.

A colorimeter or hardness test strips measure water hardness.

Dissolved Oxygen (DO)

Dissolved oxygen (DO) refers to the amount of oxygen dissolved in water. Dissolved oxygen gets into water from direct atmospheric absorption, a byproduct of plant photosynthesis, and from groundwater discharge.

Dissolved oxygen is one of the most significant indicators of water quality in water treatment systems and aquariums, and therefore, it is a crucial water quality parameter to monitor because it determines if water is polluted. If oxygen levels dramatically drop in aquatic environments, aquatic organisms cannot survive.

When DO levels drop below 3 ppm, they start to become lethal for fish. Increases in temperature, decaying organic matter, and drastic weather changes are the main causes of drops in DO levels

But, if DO is high in water, rest assured, the water quality is also high. However, while high DO levels improve the taste of drinking water*, it can corrode water pipe systems.  

*Drinking water should have a DO concentration above 6.5-8 mg/L and between 80-120%.

Many factors affect DO levels in the water, but changes in the temperature of the water are the most common, followed by salinity and pressure. One thing you do not have to worry about is dissolved oxygen affecting the pH level of the water. As there is no physical-chemical connection between the two, they do not affect one another. 

Dissolved oxygen is measured using an electrochemical DO meter and probe or the Winkler method.

Dissolved oxygen probes measure the amount of oxygen that diffuses across a permeable (or semi-permeable) membrane. Because dissolved oxygen has an inverse relationship with temperature, probes should be calibrated before each use. Salinity levels must also be closely monitored alongside DO. ​​When salinity levels increase, DO exponentially decreases

Biological Parameters

Biological water quality parameters look at the characteristics to describe the presence or absence of waterborne pathogens and other microbial organisms.

Bacteria

Bacterial content tells us a lot about water quality. Bacteria are small, single-celled organisms that can rapidly reproduce if the pH level and temperature of the water allow. Unfortunately, as bacteria multiply at such a rapid rate, they are almost impossible to measure. Yet, what we do know, is that bacteria reproduce at a much slower pace in colder environments and areas that lack nutrients.

If the water contains a high number of bacteria, the water soon becomes unsafe, harboring waterborne diseases such as typhoid and cholera. 

Algae

Algae are microscopic aquatic plants containing chlorophyll (photosynthetic pigments). They feed off inorganic material, converting it into organic material via photosynthesis.

Algae can indicate poor water quality, and many algal indicators are used in water systems to assess environmental conditions. Algal blooms are indicators of bad odors and poor taste in water. Also, as some algae species (for example, blue-green algae) can pose serious health risks, algae should be monitored when assessing water quality.

Nutrients

Nutrients are closely related to algae. As water nutrients (particularly nitrogen) increase, excessive algae growth could occur, thus depleting the oxygen level.

Viruses

Viruses are a prime cause of human waterborne and water-related diseases. Testing for viruses in the water tells us a lot about the quality of water, and if the water needs treatment before use.

Testing for viruses requires powerful electron microscopes or PCR testing methods. PCR methods are preferred because they can rapidly detect all the virus groups that cause waterborne diseases.

Despite the difficulty in testing and treating viruses in water, they are usually removed during water purification and disinfection processes.

Summary

When treating water, knowing the three main water quality parameters and principle indicators is essential. Whether your water has low pH levels, high total dissolved solids, excessive nutrients, or a strange odor or taste, there are many water pollution solutions to improve the water quality. 

If you have any questions regarding water quality or which testing kits we have to offer/will best suit your testing needs, please contact the world-class team at Atlas Scientific.

pH Probes & Sensors

Dissolved Oxygen Probes & Sensors

Conductivity Probes & Circuits

Temperature Probes & Sensors

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