We all know the best water sample testing method: take off your shoe, and dip your foot into the water. You should be able to tell if it is freezing, hot or just perfect... to your preference, though! But wait, how do you know if it is acidic? Or alkaline? Hmm, maybe there is a more scientific and accurate ...and safe way to test the water sample?
Some characteristics of water can be observed through taste, colour and smell. Still, official methods and observations are the most reliable form of establishing its properties and fitness for various uses.
The purpose to differentiate between different water samples is to give you a better understanding of occupational health and safety issues, industrial hygiene, and the environment. We'll learn about the parameters taking into account in water sample testing, the types of testing that exist, and some examples.
The Definition of Water Sample Testing
Water sample testing analyses water samples to determine their physical and biochemical properties.
Water samples are taken from different locations within the water distribution system, including water treatment plants, storage tanks, tap water, or a natural spring. The water is then tested for the presence of specific contaminants.
Water sample testing is integral to water quality management and helps ensure that drinking water is safe for use or consumption.
Water testing can be done for a variety of reasons. For the most part, the reasons are:
- assessing water quality
- investigating water pollution
The Purpose of Water Sample Testing
Water nowadays can come from various sources, including ditches, streams, or treatment plants. Sometimes, this water can be contaminated. It may come in contact with bacteria, dissolved metals, viruses, household and plant sludge, or other elements that may prove harmful once ingested by humans.
When talking about contamination, we are referring to average human tolerance levels, as different species have different tolerance levels for different types of contamination. Within the human population, people will also have varying degrees of tolerance to specific contaminants, depending on previous exposure and general health, such as liver health.
Depending on the water body being tested, different water quality indicators may be of more concern than others.
Water can be collected and tested for microorganisms or other particles in such scenarios.
| Intended use for the water body | Important characteristics |
| Agricultural use | Water pH (alkalinity), nutrient levels (soluble salts, nitrogen), microbial quality (presence or absence of pathogens). |
| Recreational (e.g. swimming, diving) | Microbiological makeup (viruses and bacteria). |
| Food & drinks | Suspended solids, toxicants (pesticides, metals), nutrients (phosphorous and nitrogen). |
Table 1: Examples of important parameters taken into account when testing a water body for different intended uses.
Common contaminants that are harmful to human and sometimes animal health include:
- Escherichia coli (E. coli) bacteria: mostly from human and animal faeces (including pets).
- Arsenic: a chemical both naturally occurring and resulting from industrial processes, which causes health complications such as cancers.
- Other heavy metals, such as lead and aluminium: can lead to several severe effects on the body, such as organ failure or damage, nervous system issues, cancers and even autoimmune disorders.
- Fertiliser runoffs, like nitrates and phosphorous: excessive consumption of these chemicals can cause severe health defects in humans like blue baby syndrome. They also harm the environment, causing water pollution (which can kill fish and other aquatic organisms).
Water Sample Testing Parameters
Water sample testing parameters indicate the water conditions or characteristics that are being tested. The main parameters can be grouped into three main categories.
| Water parameters | Details |
Chemical parameters | pH, dissolved oxygen, metals, heavy metals, total dissolved solids, etc. |
Physical parameters | Conductivity, resistivity, effluent analysis, etc. |
Microbiological parameters | Coliforms, E.coli, Enterococci, Staphylococci, etc. |
Table 2: The main water parameters tested and some examples.
The main parameters tested are pH, temperature, dissolved oxygen, total dissolved solids (TDS), conductivity, turbidity, and phosphates. These water sample testing parameters are essential to water quality because they indicate what is in the water and how it might affect aquatic life or human health.
- The pH measures the acidity or basicity of a water sample.
- Temperature is a measure of the water's heat content.
- Dissolved oxygen measures the amount of oxygen that is dissolved in a water sample.
- Conductivity is a measure of the water's ability to conduct electricity.
- Turbidity is a measure of the water's suspended particulate matter.
- Phosphates are nutrients that can cause excessive growth of aquatic plants and algae.
In addition to these basic water quality parameters, other water sample testing parameters that may be measured depending on the water quality issue being investigated include nutrients (nitrogen and phosphorus), metals (such as iron and lead), and chemicals (such as pesticides and herbicides).
Types of Water Sample Testing
Several methods can be used for water sample testing, including chromatography, spectroscopy, filtration, gravimetric analysis and titration. The most appropriate way will depend on the type of information required.
For example, water samples can be tested for pH levels, dissolved oxygen levels, dissolved nutrients, suspended solids, bacteria, the presence of certain pollutants, as well as conductivity.
The places where water can be tested include:
Chromatography
This water testing method passes a water sample through a column of absorbent/porous material. The contaminants are then separated based on their affinities to the absorbent material.
The smaller water molecules can pass through the pores more easily than the larger ones, so they are separated from the rest of the water.
This process can be used to purify water or to test for contaminants.
Chromatography columns are made from various materials, including glass, plastic, and porous clay. The type of column that is used will depend on the specific application.
Using these instruments, researchers can trace and analyse contaminants, trace metals, and potential pollutants, such as pharmaceuticals and solvents. Chromatography highlights all these substances, even in barely traceable concentrations.
Spectroscopy
Chromatography is often used in conjunction with spectroscopy, which helps to identify better the presence of various substances in a water sample, including metals.
Spectroscopy is a water sample testing technique that uses lasers to measure the concentration of various substances in a water sample.
The laser beam is passed through the water sample, and the resulting light is analysed to determine the concentrations of multiple substances. This information can then identify water contamination and determine its source.
Spectroscopy is an essential tool for water quality testing, and it can be used to monitor water contamination levels over time.
Filtration
Water samples can be filtered for microbiological testing or inorganic compounds. This typically involves using a porous membrane that lets water pass through but captures microorganisms or compounds for further viability analyses.
A cellulose membrane filter can be used to capture water microorganisms. It can be placed on a Petri dish after the water has passed through it to grow cultures, from which water microbiological quality can be assessed.
Gravimetric analysis
The gravimetric analysis determines the concentration of a chemical substance in water by measuring the weight of a water-insoluble compound precipitated from the water.
In other words, this is done by weighing the water sample before and after evaporation. The difference in weight is used to calculate the number of dissolved solids in the water sample.
The most common reason for water testing is to measure the concentration of a particular contaminant, such as lead or mercury. However, water testing can also measure the concentrations of nutrients, minerals, and other chemicals in the water.
Gravimetric analysis is generally more accurate than other water testing methods, such as spectrophotometry or titration. However, it is also more time-consuming and requires more expensive equipment.
Titration
Titration is the process of adding a small quantity of one chemical solution to another until the desired reaction occurs.
This is typically done to determine the chemical concentration in a water sample. The most common type of water sample testing through titration is acid-base titration. This involves adding an acid to a water sample until the pH of the water reaches the desired level.
The acidity or alkalinity of water is measured on a pH scale, with seven being neutral, less than seven being acidic and greater than seven being alkaline.
Although titration is typically used to determine an inorganic chemical's concentration in water, it can also be used to determine the concentration of other substances, such as fats or proteins.
Examples of Water Sample Testing
Once the water samples have been collected, they are typically sent to a laboratory for analysis. The results of water sample testing can provide valuable insights into an ecosystem's health and help identify potential environmental problems.
Samples are kept in sealed containers at low temperatures to prevent the growth of bacteria during transportation and before it is analysed in a laboratory. The general steps followed for taking and testing an environmental water sample are:
Make observations - At the collection site, note what you sense through hearing, smell, sight, etc.
For example, what organisms use the water source (crows, sheep) if they enter the water (bathing, cooling feet, drinking), and what lives inside the water (fish, crustaceans)?
Notice the plants in the area (grasses, trees, seaweed), the water level (whether it changes), bank stability, and how the water body being observed is affected by the environmental factors during observation times (temperature, rain, harsh sunlight). A calm environment (no turbulent weather patterns) and little water usage, for example, by cattle, are the best for water sampling.
Please remember:
- Water movement: if the water is static, create circular motions, or if the sample is taken from a tap, leave the water flowing for a few seconds first so that the sample won't be taken from stagnant water.
- Store the collected water at less than 10 degrees Celsius, but do not freeze them. They should ideally not be kept for more than 24 hours.
Water Sample Testing - Key takeaways
Water's physical and biochemical properties can be established through water sampling techniques.
Different occupations have different water quality standards. Agricultural water use in the UK will allow a low percentage of naturally occurring e-coli bacteria when watering crops, but bottled water standards won't.
Groundwater, surface water, municipal water supplies, or tap water can be used to take water sample readings.
Chromatography, spectroscopy and titration are a few methods that help identify water quality.
The most simple water sample testing method establishes turbidity, pH and temperature.
References
- How Can Chromatography Help with Clean Water, 2021, https://www.chromatographytoday.com/news/liquid-chromatography/65/breaking-news/how-can-chromatography-help-with-clean-water/55693. Accessed 17.07.22
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