Water Turbidity: Causes & Measurement & Management [Complete Guide]
Water is a very limited resource and should be handled with great care. Because only 2.5% of all water on earth is unsalty fresh water. Also, only 0.3% of this water is in liquid form on the surface.
So, we don’t have the luxury of wasting fresh water that is available to us. We should reserve it with the utmost care and use it as efficiently as possible.
Unfortunately, this is not how we treat our water resources. Human activities and negligence have been greatly affecting the availability and quality of freshwater.
Although there are many reasons that lower the quality of water, in this post we will be focusing on turbidity. Because it has both short-term and long-term negative health impacts on humans as well as aquatic life.
What is turbidity?
Turbidity is an optical property of water defined as the amount of light that is scattered when passed through a sample. It is often used as a surrogate for the amount of suspended sediment or particulates in the water.
The higher the turbidity of a body of water, the lower its transparency. This is because the particles in the water tend to reflect and scatter light, reducing the intensity of light reaching the other side.
Water with high turbidity is usually referred to as being ‘murky’. Although, the official scientific term for water with extremely high levels of particles in suspension is hyper-turbid water.
The turbidity of water varies greatly depending on the season, amount of rainfall, and other environmental factors. Rivers that carry a lot of silt and mud eroded from the soil become very turbid during the rainy season.
Although turbidity is a natural phenomenon, human activities can significantly increase it.
Activities that cause soil erosion around the river, such as deforestation or agricultural practices that leave fields with little vegetation can result in high levels of turbidity.
What are the causes of turbidity?
There is always some degree of turbidity in water. However, human activities and negligence can significantly increase the degree of turbidity in water bodies.
Here are some of the main causes:
Growth of phytoplankton
Phytoplanktons are microscopic organisms that live in water bodies. The types of phytoplanktons that proliferate in rivers will depend on the environmental conditions in the river at a specific time. When the levels of nitrates or phosphates are high in rivers, algae tend to proliferate.
Phytoplankton is always present in water, but when their numbers increase due to conditions that favor growth, the degree of turbidity also increases.
During construction work, the soil is often removed from the area that is being developed. If the soil is not properly removed or disposed of, it ends up in rivers. The soil then settles in the river and decreases its overall transparency.
The rainy season causes the water in rivers and lakes to rise in volume and carries with it a lot of debris. This causes short-term turbidity in water bodies, which may last for several weeks or months depending on rainfall levels.
Forestry work to provide space for agricultural fields or housing projects leads to more soil being eroded by rainwater.
The eroded soil flows into the river and causes an increase in turbidity levels downstream of the deforestation activity. As a result, the soil and mud in the area will flow into rivers causing them to become turbid.
Agricultural practices that leave fields without vegetation cause a large volume of soil to be eroded and deposited downstream. This leads to an increase in turbidity levels downstream, as well.
Mining is another human activity that can impact turbidity levels in river water. During mining, the ore is crushed and the smaller particles are created. These particles are then carried by the rains into lakes and rivers, where it increases turbidity levels.
Water reservoirs created through the construction of dams can significantly increase turbidity levels downstream.
The reservoirs are designed to hold water that is used for industrial, agricultural, or domestic purposes.
When the level of water drops in the reservoir, it causes sediments on the floor of the reservoir to be lifted up and to flow downstream, further increasing turbidity levels.
Animal waste contains nitrogen and phosphorus, which can cause an increase in the number of phytoplankton that grow and proliferates in bodies of water. This, in turn, results in increase turbidity levels.
Especially during hot weather, the number of animals will more often than not increase near rivers and lakes because of the availability of water and vegetation. As a result, there will be more animal waste around these bodies of water, which will ultimately lead to an increase in turbidity levels.
Polluted wastewater can also increase turbidity levels. Industries and factories can pollute rivers with toxic chemicals, which lowers the ability of the light to penetrate the water and increases turbidity levels.
Turbidity caused by toxic chemicals is the most dangerous form of turbidity. Because the problem is not turbidity anymore, but a toxic chemical that can cause diseases and even death.
What are the effects of having high turbidity levels?
The effects that high turbidity levels can have on rivers are quite serious. Here is a closer look at some of the most important issues:
Reduces water transparency
When there is sediment suspended in the river, the light cannot penetrate deeply into the water, phytoplankton cannot grow in large numbers, which reduces the oxygen supply for fish.
The reduced sunlight penetration also prevents underwater plants from photosynthesizing, preventing them from performing other important functions related to the river ecosystem.
Higher turbidity levels can also decrease the amount of dissolved oxygen in the water, which makes it more difficult for fish and other organisms to breathe.
Prevents effective sheltering
Turbidity levels that are too high or too low can harm aquatic organisms, causing them to be unable to effectively shelter themselves.
For example, when turbidity is extremely high, it can blind fish and other creatures that live underwater, preventing them from finding food sources and shelter.
Prevents successful development of fish eggs and larvae
Extremely high turbidity levels prevent fish eggs and larvae from developing successfully. This is due to the fact that they rely heavily on light penetration, which reduces substantially when there are suspended particles in the water.
Impact on drinking water supply
The turbidity levels in rivers influence what type of water treatment methods will be needed before the water can be used.
If the turbidity levels are too high, it may not be possible to use conventional filtration and chlorination techniques to treat the river water and make it potable for human consumption.
How the turbidity of water is measured?
Turbidity can be measured using a few different methods either in a laboratory or in the field using specialist optical equipment.
Here are the most common methods that are used for turbidity testing:
The Formazin Turbidity Units (FTU)
The Formazin Turbidity Unit (FTU) is the most common turbidity measurement method. ISO abbreviates its units as FNU (Formazin Nephelometric Units).
ISO 7027 specifies the procedure for determining turbidity in water quality. It measures the incident light scattered at right angles from the sample to calculate the number of suspended particles in a sample of water.
With this method of measurement, a photodiode captures the scattered light and converts it to an electronic signal, which is then transformed to turbidity. Using an Arduino microcontroller and affordable LEDs, open-source hardware has been constructed to detect turbidity reliably using the ISO 7027 technique.
The Nephelometric Turbidity Unit (NTU)
The NTU is measured using an electrical instrument known as a nephelometer. The water to be measured is placed in a standard container.
A light beam goes through the water and contacts a sensor on the other side of the container. The turbidity of the water is calculated from the strength of the signal received from the sensor.
A second sensor, situated at right angles to the beam, measures light dispersed by particles in the water. The two readings are used to calculate the turbidity of the water. NTU is the most common unit used for measuring turbidity in environmental studies.
To calibrate the instrument, a standard solution is required. A commonly used calibration fluid has a concentration of 0.5 NTU. It is important to use the same calibration fluid at all times, as small changes can have a significant effect on the readings produced.
Jackson Turbidity Units (JTU)
Jackson Turbidity Unit is a historical unit used for measuring turbidity, which is not much used today. With this method, a water sample is passed through a glass tube until a flame underneath the tube could no longer be seen.
It is the inverse of the length of a column of water required to totally conceal a candle flame viewed through it. The cleaner the water, the more water required (the longer the water column).
Of course, water alone produces some attenuation, and any color-producing compounds dissolved in water can attenuate particular wavelengths. Although candles are no longer used in modern equipment, this method of attenuating a light beam through a column of water is still used in some instruments.
The Total Suspended Solids (TSS)
Total suspended solids (TSS) are the dry weight of non-dissolved suspended particles in a sample of water that can be caught by a filter and quantified using a filtration device.
It is also known as total suspended matter (TSM) which is a water quality metric used to evaluate the quality of any sort of water sample. TSS is usually measured in milligrams per liter (mg/l).
TSS is not directly related to turbidity. Because turbidity refers to an optical property of water, while TSS refers to a mass concentration. However, it can be approximated (at least theoretically) that the higher TSS found in water, the higher turbidity will be.
A Secchi disk is a weighted, white, or black disk that measures the depth of water by how far it can be seen. It is lowered into a lake until the observer on the side can no longer see it. The depth is then recorded as a measure of water clarity.
The color of the water, algae, and suspended sediments can all have a significant impact on the ability to detect the disk in water. The amount of light scattered can vary even if turbidity is not changing, making it challenging to compare different measurements.
A Secchi disk measurement should always be done between 9:00 and 15:00 on the shaded side of a boat or dock. The optimal time to get the finest outcomes is between 10:00 and 14:00.
Another way of measuring turbidity using a Secchi Disk is to lower the disk after it vanishes. Then, the depth at which the disk reappears again indicates water turbidity. Using this method, multiple measurements should be made in order to get a good estimate of the average turbidity.
What types of light are used in turbidity measurements?
Turbidity measurement is typically conducted using a light source that is scattered by particles in the water.
There are three main types of light sources used in turbidity measurements:
White light is the most common type of light used in turbidity measurements. It is emitted by an incandescent light source and is better suited for detecting tiny particles. Therefore, it is preferred in applications that measure low turbidity levels.
Infrared Light Source (EN ISO 7027)
Infrared light is a type of light source used in turbidity measurements. It is emitted from a black body radiator, which absorbs all electromagnetic radiation except for that of a certain range of wavelengths, and then emits it as a broad spectrum.
Using the EN ISO 7027 method, a single wavelength of light is chosen and transmitted through the sample. The power of the emitted light at this same frequency, as well as the attenuation factor, are then measured.
The turbidity of the water is then calculated using an equation that accounts for the wavelength used, the transmitted intensity of this light through the sample, and attenuation factors.
Laser light is the most accurate and consistent of all light sources used in turbidity measurements. It is the best choice for measuring and assessing very small changes in turbidity.
Therefore, it is used to monitor the effectiveness of filters that produce ultrapure water, which is commonly employed in many industrial processes.
What are the challenges in turbidity measurement?
There are many reasons why turbidity measurements may not be reliable. Here are some common issues that can affect turbidity readings:
Inconsistent Light Intensity
Different light sources emit different wavelengths of light, which can alter the results of a measurement. When a light source is not consistent enough as suggested by the measurement, it can cause effects such as varying turbidity readings and inaccurate data.
Inconsistent Light Source Angle
If the angle at which light is transmitted through water is not consistent, then any measurements made may not be accurate.
Poorly Maintained Measurement Instrument
A poorly maintained instrument can affect the outcome of turbidity measurement. For example, dirt on optics may distort light signals and reduce the accuracy of readings.
Also, if parts are worn or broken on an instrument, it could skew the results of any measurements taken by that device.
Inconsistent Water Samples
Water samples are not always consistent. If factors such as temperature, salinity, and pH levels of water samples change during a measurement, then turbidity readings may vary over time. Also, the type of particles in the water can change depending on where they came from.
If glassware used to hold water samples are not consistent, then turbidity measurements may be inaccurate.
Different types of glassware have different thicknesses and coloration, which would affect the turbidity of a sample. Also, if the inside and/or surface of a container is not perfectly smooth, then it can cause light to scatter and affect results.
Inconsistent measurement practices
Even if an instrument is in good condition, the way in which measurements are made can affect the outcome of a test.
For example, if when performing multiple turbidity measurements on one sample, different amounts of time are used to wait between each reading, or if different amounts of time are allowed to pass before moving on to the next sample, then the results will vary and be inconsistent.
Also, a lot of times a single measurement may not be enough to achieve accurate results. Multiple measurements must be taken and averaged together to calculate a more accurate reading.
Tests should be done at the exact same point and time of the day, with the same number of samples.
The people who are in charge of turbidity tests or analysis should be well versed in the instrument being used to take measurements.
They must have a good understanding of how light propagates through water, and they must know the proper calibration procedures for the device.
In addition, if quality control measures are not followed during analysis, readings may be inaccurate or not representative of true values.
Why are turbidity measurements important?
Turbidity measurements are used to determine the clarity of the water. It is a major indicator of water quality and is very important in many industries. If you have been wondering what industries use turbidity measurements here are some examples:
Water Treatment Plants
Water treatment plants use turbidity measurements to ensure that the water is of good quality before it is sent out to customers. With proper testing, water treatment plants can also ensure that the water is safe to drink.
Water quality can also affect the taste of water, so certain areas may have to put up with an unpleasant tasting supply of drinking water. Also, If the water has high turbidity, then it can cause consumers to get sick with things like stomach cramps, diarrhea, and vomiting.
Turbidity measurements are also used to study aquatic habitats. If a researcher is observing a particular ecosystem, they may take turbidity measurements in the water to see if there are changes in the environment.
If an area has been polluted, then turbidity measurements would indicate that the water quality is poor and that there has been a disturbance in the ecosystem.
Turbidity measurements can be used to determine how well industrial processes are working.
For example, in food processing facilities, turbidity measurements can be used to ensure that the water is clean enough for use. If the water has high turbidity, then it may need to be filtered or purified before being used.
There are so many industries that use turbidity measurements to ensure the quality and safety of their manufacturing processes.
Some of these industries don’t even target improving water quality for consumers. But they use it for their own purposes like testing their equipment and processes.
How to remove turbidity from water?
Since turbidity is a measure of the cloudiness or haziness in water caused by suspended particles, one can try to remove these particles from their water.
If you have been wondering how to get rid of turbidity in your water, here are some things you can do:
Gravity filtration is simple and cheap but can take a lot of time if you are trying to purify large quantities of water.
Sedimentation is the process where the particles settle at the bottom of an area filled with turbid water through gravity or slow-moving currents. This method is quite primitive but probably the least expensive.
It can be used to remove particles in water that have large sizes. However, it does not catch everything. So, if you are wondering how to remove turbid water quickly probably this method is not what you are looking for.
Cloth filtration is done through a straining cloth that catches particles suspended in the water. This type of filtration can remove a high percentage of particles from the water, but it is still a primitive method for consistently purifying the water.
Sand filtering removes suspended materials, floating and sinkable particles through an area filled with sand.
This method is better than cloth filtration because the particles are caught in layers of sand, giving the water a better contact time for the particles to settle. Mos sand filters use different layers of sand made of different granule sizes. This allows the water to go through a couple of layers before being filtered.
Sand filters are popular since they are simple and easy to maintain. However, they need regular backwashing or cleaning because the particles can get clogged in the sand.
Moringa tree flocculation uses Moringa tree seeds when crushed acts as a natural flocculant. The seeds are shelled and ground with a crusher mill. They are then added to water to remove particles from the water.
Once the particles are in the water, users let the water and moringa seeds settle for 24 hours before decanting them into another container.
Although this method is not a substitute for modern methods of water treatment, it is a good option for those living in remote areas where flocculation equipment or filters are not readily available.
Moringa considerably reduced the turbidity of water in laboratory studies, but it also significantly raised the chlorine demand of the water due to organic matter present in the seeds.
Therefore, it is best to use moringa only in emergencies since it cannot be used for regular water treatment.
The cactus raket in Haiti provides a natural flocculant. Users select the raket, cut it diagonally to expose as much flesh surface area as possible, add the raket to the water, stir briefly, and wait 10 minutes before filtering the water through a towel.
Although this method works, it is not a modern water treatment method and can only be used where the cactus raket is abundant.
Aluminum sulfate is commonly used in water treatment plants as a flocculant. It is commonly referred to as “alum.” and is readily available in naturally occurring mineral blocks of soft white stone.
In many laboratory research, the application of alum greatly reduced water turbidity and also significantly lowered the chlorine requirement of turbid waters.
Alum is used as a flocculant in a variety of ways like stirring it into the water, dropping stones into the water, or adding a small amount of alum directly to a cloth filter.
It is an inexpensive water treatment technique that minimizes turbidity. However, the alum added to the water might change the pH of the treated water, which can lead to poor water quality.
Cartridge filters remove particles through a filter media (porous paper, ceramic, sand, etc.) placed in a cartridge. Cartridges are made up of several sections that trap the particles in multiple levels of media.
This type of filtration is the most commonly used for small-scale water treatment like home purification systems.
Reverse osmosis (RO)
Reverse osmosis (RO) is a method that uses pressure to drive water through a semi-permeable membrane to remove the vast majority of impurities. It works by forcing water into a membrane that blocks dissolved impurities, including salts and other particles.
The amount of pressure needed for RO systems can vary depending on the level of impurities in the water. However, RO systems require a lot of energy and regular maintenance. Therefore, they are also not suitable for small-scale purification systems.
Membrane filter (microfilter)
Membrane filters use a thin film membrane that has pore sizes of 0.1 – 10 microns making them very effective at removing particles.
They are very effective at removing turbidity. However, these filters are expensive and are not readily available in developing countries.
Microfiltration is a pressure-dependent technique that removes dissolved particles and other compounds from water to a lower extent than nanofiltration and reverse- osmosis.
Distillation is the process of boiling water and capturing its vapor, leaving behind impurities. This method requires a large amount of energy to boil water. Therefore, it is not a proper method for removing turbidity from water unless no other alternative is available.
Is high turbidity in drinking water a problem?
Some amount of suspended particles in your drinking water isn’t necessarily toxic or harmful. Although there may be unpleasant taste, odor, and reduced clarity may be an inconvenience.
Our bodies can handle low levels of turbidity. However, high levels of turbidity in drinking water already become more than an aesthetic problem. Therefore, The WHO recommends drinking water turbidity levels ideally to be less than 1 NTU and not exceed 5 NTU.
Consuming high levels of turbidity in water can have negative effects on your health. An excess of suspended particles in the water can irritate your gastrointestinal tract, causing an upset stomach, nausea, vomiting, or diarrhea.
It can be especially harmful to those with already compromised immune systems or certain gastrointestinal disorders.
Therefore, it is important to be aware of the turbidity levels of your drinking water so you can take steps to filter it to reduce the health risks.
Is turbidity the same as other water contaminants?
No, although turbidity and many other contaminants can both contribute to poor-quality water, they are two different things.
Turbidity is the cloudiness, haziness, or murkiness that you see in the water. It can be caused by various things including natural deposits, eroded soil and sediments, decaying plant and animal life, and man-made pollution.
However, contaminants in the water may also be one of the reasons for increased turbidity levels.
What is the turbidity level for a water body to aquatic sustain life?
Most aquatic life requires a certain level of clarity in the water. If the turbidity is higher than this, their health is at risk.
That said different aquatic organisms require different minimum turbidity levels to survive. Therefore, a blanket statement cannot be made on the turbidity level for a water body to sustain aquatic life.
However, to give you a better idea here are the required turbidity levels for some common aquatic life as defined by Minnesota’s water quality regulations:
|Classes (and descriptions)||Turbidity (NTU)|
|1B (drinking water)||10|
|2A (cold water fishery, all recreation)||10|
|2B (cool/warm water fishery, all recreation)||25|
|2C (indigenous fish, most recreation)||25|
Turbidity is an optical characteristic of water but gives an important insight into the overall health of a water sample. Although all water has a certain level of turbidity after a certain threshold, it becomes more of an issue that must be taken into consideration.
It may occur in water naturally in certain seasons or conditions or is caused by man-made pollution such as wastewater contamination, mining operations, improper agricultural practices.
High turbidity levels affect the taste and the appearance of water but can also pose a risk to your health if it is not filtered properly.
If you notice high turbidity in your drinking water supply or nearby waterbody, it is important to go beyond just looking at the turbidity level. Because the reasons that contribute to high turbidity levels can go beyond just sediment or particles in the water.