Public Lab Research note

7 Ways to Measure, Monitor, and Evaluate Water Quality

by anngneal | December 08, 2017 12:23 08 Dec 12:23 | #15332 | #15332

Healthy water bodies significantly affect the underwater flora and fauna and the overall health of the environment. Numerous physical, chemical, and biological factors affect the quality of water in the ponds, the lakes, the streams, the rivers, the oceans, and the groundwater.

Effective and pre-emptive water-quality monitoring strategies can help environmentalists determine the natural and human factors that affect the water bodies. The results can be used to plan restoration projects to ensure that the water bodies meet the environmental standards.

Here are seven ways to measure and monitor the water quality, encouraging a clean and healthy aquatic ecosystem.

1. CDOM/FDOM Monitoring

Coloured or chromophoric dissolved organic matter (CDOM) occurs naturally in water bodies. This organic matter absorbs the ultraviolet light and decomposes to release tannin, an organic pollutant that causes the water to turn murky. Moreover, tannin contributes to reducing the pH (acidic) of the water and depleting the oxygen levels.

A portion of the CDOM fluoresces and is referred to as fluorescent dissolved organic matter (FDOM) further making the water look cloudy.

CDOM/FDOM levels can be measured using electrical optical sensors that use fluorometers and sapphire lens. These sensors gauge the light availability in water bodies depending on the water level and indicate the concentration of dissolved organic matter (DOM).

2. Chlorophyll Fluorescence Analysis

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When the surface water in ponds and lakes is rich in minerals, namely phosphorus and nitrogen, algae flourish. Disproportionate growth of algae leads to oxygen depletion and increased levels of nitrogen and phosphorus which can be toxic to the flora and fauna.

Chlorophyll fluorescence, measured using algae toximeters, indicates the percentage of wet-chemical chlorophyll and active chlorophyll in the water sample under illumination. This is an effective method to keep a check on the excessive algal growth and monitor the water quality.

3. Conductivity, Salinity, and TDS Monitoring

The conductivity of a water body is an early indicator of the water quality. Conductivity affects the salinity and total dissolved solids (TDS) content, which in turn affects the concentration of oxygen in the water.

Certain ecological (temperature, excessive rainfall, and increased organic matter content) and man-made (pollution) factors can increase or decrease the water bodies' conductivity, severely impacting the water quality.

For instance, an oil spill or increased levels of organic substances in an ocean can decrease its conductivity, indicating water pollution.

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Conductivity, salinity, and TDS meters analyze the water quality by measuring the specific electrical conductance of electrolytes dissolved in the water. Though each of these instruments measures a separate parameter, the results are correlated and indicative of pollution.

4. Recording the Water Temperature

Temperature is a crucial factor that affects the other water quality parameters such as, the rate of photosynthesis and metabolism, the dissolved gas concentrations, the conductivity and salinity, the pH, and the water density amongst other factors.

For instance, ammonia at a high pH is toxic to plants and aquatic animals, however, a sudden change in temperature can double the impact.

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Several devices such as thermometers, thermistors, thermocouples, and digital temperature sensors are used to obtain temperature readings at varying depths, time, and locations.

5. Measuring the Dissolved Oxygen Levels

The dissolved oxygen (DO) is a measure of the amount of oxygen available to the flora and fauna and is reported as percent saturation or mg/L. The oxygen levels in water go down owing to the decomposition of organic material such as dead plants and animals and human wastes. A dissolved oxygen level of less than 6 mg/L can be harmful to the ecosystem of water bodies.

The dissolved oxygen concentration can be measured using the electrochemical or optical sensor, the colourimetric method, the Winkler titration method, and the optical dissolved oxygen sensors.

6. pH and KH Testing

An increasing pH level is dangerous to the ecosystem of the water body. A safe pH range for a pond or a lake is between 6.0 to 8.0; however, certain factors such as overgrowth of algae and pollution alter the pH of the water and increase the levels of toxic ammonia.

pH can be tested using water test kits that are color-coded and offer a wide range of pH measurement. These kits work best to give you an idea of the pH range the water falls into. However, for accurate pH measurements, electronic pH sensors offer measurement values up to two decimal points.

KH or the carbonate hardness (a measure of carbonate and bicarbonate levels) is another factor that needs to be monitored as it significantly impacts the pH of the water. Therefore, to readjust the pH, you may often have to stabilize the water KH.

7. Assessing the Turbidity, TSS and Clarity

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The solar radiation provides light, heat, and energy to all living being on earth. Low or high levels of ultraviolet radiations can halt the photosynthetic process, causing permanent damage to the aquatic ecosystem.

Suspended solids, decaying vegetation, and other dissolved colored material cause the water to appear cloudy and murky, impacting the penetration of sunlight on water and the aquatic life.

A sudden increase in the turbidity and the total suspended solids (TSS) is an indicator of soil erosion and point-source pollution adding heavy metals and effluents into the water.

A nephelometer is used to measure the scattered light at an angle of 90◦ and the results are reported in Nephelometric Turbidity Unit (NTU). The total suspended solids are measured by filtering and weighing the sample and are measured in milligrams of solids per liter of water.

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The Secchi disk is often lowered in a water body to measure the depth until which it is no longer visible (also referred to as the Secchi depth). This is a measure of the cloudiness of the water.

These devices help measure the water clarity and photosynthetically active radiation (PAR), promoting a healthy environment for the plants and animals residing in the water body.

By measuring and monitoring the key indicators of the quality of water, researchers and environmentalists can plan and execute strategies to conserve the water bodies and encourage biodiversity. The aforementioned methods will help you evaluate the various parameters that determine the water quality in freshwater and brackish water bodies.

Useful Additional Info

  1. Iperovich's insightful research on faster-waterproofed temperature sensors
  2. Accuracy of long thermistors
  3. Policies for Tackling agricultural water pollution in England
  4. Department forEnvironment Food and Rural Affairs standards to protect the water environment
  5. Water quality assessment of lake water: a review


I would add the following: alkalinity, hardness, and perhaps ORP

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Great work and super useful for citizen's looking to track the quality and state of open water. We've been looking into something like this for drinking water at

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