Types of Water Quality Tests, Equipment and Analytical Methods
The measurement of water quality is a very exacting and time-consuming process, and a large number of quantitative analytical methods and instrumentations are used for this purpose.
Portable, Handheld, and Benchtop instruments are available to test parameters including pH, conductivity, hardness, colour, turbidity, odour, taste, oxidation-reduction potential (ORP), dissolved oxygen and CO2, total dissolved solids (TDS), suspended solids, total hydrocarbons (TH), and other water quality characteristics.
Multiparameter analyzers, which are capable of measuring various user-selectable parameters, waterproof instruments, and meters that can test from only a few drops of water are also available.
Testing procedures and parameters may be grouped into categories such as physical, chemical, bacteriological and microscopic:
• Physical tests indicate properties detectable by the senses.
• Chemical tests determine the amounts of mineral and organic substances that affect water quality.
• Bacteriological tests show the presence of bacteria, characteristic of faecal pollution.
In industrial water conditioning, chemical analyses are needed to govern the treatment processes. The analysis should be conducted promptly after sample collection so that the chemical nature of the sample does not change.
In order to ensure that results obtained from an analysis are useful, it is necessary to secure a representative sample from the system to be tested. Sample lines must be flushed before samples are taken, and all sampling locations and procedures must be well defined.
For most tests, the samples should be cooled to room temperature (21-26°C, 70-80°F) prior to testing. They should also be filtered through 0.2-2.5 µm filters if required.
Commonly conducted water quality tests include:
Testing the temperature helps determine the rate of biochemical reaction in an aquatic environment and indeed whether they are able to occur at all. If the water temperature is too elevated, this can limit the water’s ability to hold oxygen and decrease organisms’ capacity to resist particular pollutants.
Measures the acidity of water. Most aquatic organisms are only able to survive within a pH range of 6 to 8.
Chloride is usually present in fresh and salt water. However, its levels can be exacerbated as a result of minerals dissolving and industrial pollution
Measures the total of all non-carbonate salts dissolved in water. Measuring groundwater salinity indicates how salty your topsoil may become if the watertable rises.
Dissolved Oxygen Test
Measures the amount of oxygen dissolved in water. Without this, aquatic life is unable to conduct cellular respiration and is thus a key indicator of water health.
Measures the amount of particulate matter that is suspended in the water, or more simply, how clear the water is. If high levels of turbidity are present, photosynthesis is affected as light is unable to penetrate, increasing the water temperature.
Nitrate and Phosphate
The presence of these essential nutrients is a good indicator of strong plant life. However, the addition of artificial nitrates and phosphates through detergents, fertilisers or sewage can be harmful and result in eutrophication, generally in the form of unwanted algal blooms.
We measure whether any pesticides are present and their concentration levels.
The measurement of the reduction-oxidisation potential of a solution, which indicates the electron activity. Micro-organism growth is highly dependent on these levels.
Estimates the total amount of solids dissolved in the water. This can be a good indicator of the level of salinity.
Testing that indicates the presence of a suite of metals which are not naturally occurring in water. Heavy metals (Aluminium, Antimony, Arsenic, Beryllium, Bismuth, Copper, Cadmium, Lead, Mercury, Nickel, Uranium, Tin, Vanadium and Zinc) can find their way into water bodies through natural processes or human activities such as mining, processing of minerals, use of metals as containers and also transportation through metallic pipelines. Heavy metals are known to harm kidneys, liver, nervous system and bone structure.
Lead poisoning in humans can cause problems in synthesis of haemoglobin, kidneys, gastrointestinal tract, joints and reproductive systems and acute or chronic damage to the nervous system. Lead can also cause osteoporosis and weaken bones because it starts replacing Calcium in the bones.
Long-term exposure of cadmium leads to renal dysfunction. High exposure can least to lung cancer and osteodystrophy. Nickel has numerous reported mechanisms of toxicity including redox – cycling and inhibition of DNA repair as well as exhibiting allergic effects.
Exposure to mercury can lead to tremors, gingivitis and other psychological changes with spontaneous absorption and congenital malformation. Mono methyl mercury causes damage to the brain and the central nervous system, congenital malformations and development changes in young children. Vanadium has toxic effects on the liver, kidney, nervous and cardiovascular systems and blood forming organs.
Petroleum hydrocarbons (TRH), Monocyclic Aromatic Hydrocarbons (BTEX) and Poly Aromatic Hydrocarbons (PAHs, including benzo (a) pyrene)
The state of the water can change frequently as a result of:
• Soil entering the water through events such as erosion, land clearing and overgrazing.
• Chemicals entering the water through fertilisers, pesticides and leeching
• Pollution entering the water from the refuse of factories, sewage systems, mines and service stations
• Rubbish disposal (both small scale and from landfill)
Regular water testing can be helpful over a long period of time to monitor any changes that occur in water quality. If this occurs, it is essential that the monitoring occurs at fixed intervals from the same point. However, it can also be a good idea to conduct water testing in response to an unexpected event such as a chemical spill.
Common new methods of water analysis often involve the highly sophisticated electronic instrumentation:
• Ion Chromatography is used to measure trace levels of anions in feedwater, steam, condensate, and boiler water.
• Atomic Absorption Spectroscopy (AA), Inductively Coupled Ion Spectroscopy (ICP), X-ray Fluorescence Spectroscopy, and other laboratory procedures are used routinely to measure many elements at trace levels in a fraction of the time required for wet chemical methods. Some instruments can provide concurrent read-outs of over 40 elements in ppb measurements.
• Gas Chromatography (GC), or Gas Chromatography and Mass Spectroscopy (GC/MS), quantitatively separates and detects volatile components (e.g., neutralizing amines) in boiler condensate.
• High-Pressure Liquid Chromatography (HPLC) permits the separation and detection of trace organic compounds in antimicrobial applications.
• Total Organic Carbon (TOC) measurements are used to determine the amount of organic compounds present in water as a result of water treatments or process leaks. This process is also useful for measuring organic fouling of resinsin demineralizer systems.
• Nuclear Magnetic Resonance Spectroscopy (NMR) provides an analytical tool to aid in determining the structure of organic polymers and other organic water treatment chemicals.
• Fourier Transform Infrared Analysis (FT-IR) permits the qualitative and quantitative determination of the composition of boiler and cooling system deposits.
• Specific ion electrode detection is an electrometric method that can measure trace amounts of both anions and cations in water and is within the reach of most laboratories and testing sites.