Ammonia / Ammonium

Ammonia is a chemical compound of both nitrogen and hydrogen with the formula NH3. It is primarily sourced by and is highly toxic to aquatic life. Ammonia is a major food source to nitrifying bacteria which is deadly to fish. This makes Ammonia an important parameter to measure, any reading above 0.02 mg/l (ppm) can be considered harmful.


Biochemical oxygen demand (BOD) represents the amount of oxygen consumed by bacteria and other microorganisms while they decompose organic matter under aerobic (oxygen is present) conditions at a specified temperature.

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Chloride is one of the major inorganic anions, or negative ions, in saltwater and freshwater. Almost all natural waters contain chloride originating from salts from natural minerals, saltwater intrusion into estuaries and industrial pollution, including man-made pollutants like road salts used as a de-icer.


Chlorine occurs naturally in water and soils combined with other elements such as sodium. It is used in water as a disinfectant and can be found in drinking water, swimming pools and many water treatment systems.

CO2 / Conductivity

Conductivity (EC) is a measure of the ability of water to pass an electric current and it is affected by the presence of dissolved solids (salinity) such as chloride, nitrate and phosphate and by temperature, the warmer the water, the higher the conductivity. Monitoring conductivity can alert you to discharges or pollutants in water and soil.


Chemical Oxidation Demand (COD) is a test to measure the organic compounds in applications such as lakes, rivers or wastewater which have been contaminated by domestic or industrial waste.

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Dissolved Oxygen

Dissolved Oxygen (DO) is a measure of the level of oxygen dissolved in water. This is the amount of oxygen available to living aquatic organisms. The amount of DO in a water body is an indicator about its water quality.


Dissolved organic carbon (DOC) is defined as the total quantity of organic carbon compounds that pass through a 0.45µm filter, and represents the vast majority of organic material in most water samples.

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Low Flow Sampling

Low flow purging and sampling involves extracting groundwater at rates comparable to ambient groundwater flow, so that the drawdown of the water level is minimised, and the mixing of stagnant water with water from the screened intake area in a well is reduced.


Van Walt offers a range of multiparameter water quality sensors, meters and handheld instruments to purchase or rent. The multiparameter water quality range can measure DO (optical Dissolved Oxygen), pH, ORP, conductivity, specific conductance, salinity, resistivity, total dissolved solids (TDS), ammonium (ammonia), nitrate, chloride, temperature and turbidity.


Nitrate is a naturally occurring by-product of the breakdown of organic waste. In low concentrations it stimulates the growth of aquatic plants. At higher concentrations it can be directly harmful and can also lead to excess algae growth and eutrophication. A source of excess nitrate is surface runoff from agricultural land.

ORP / Redox

Oxidation reduction potential (ORP), also known as REDOX, is a measurement that reflects the ability of a molecule of water or soil to oxidize or reduce another molecule. It indicates possible contamination, especially by industrial wastewater. ORP can be valuable if the user knows that one component of the sample is primarily responsible for the observed value. For example, excess chlorine in wastewater effluent will result in a large positive value and the presence of hydrogen sulfide will result in a large negative value.


Soil water tension monitoring


pH is related to the concentration of hydrogen ions in a solution and is a measure of acidity or alkalinity. In natural ecosystems it can vary from around 4.5, for acid peaty upland waters, to over 10.0 where there is intense photosynthetic activity. pH 7 is considered neutral.


Phosphate (P) is a macronutrient essential for the survival and growth of organisms in aquatic systems. High concentrations of phosphate are found in agricultural fertilizers, manure and organic wastes in sewage effluent.

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Turbidity is caused by particles suspended in water that scatter the light making the water appear cloudy, it is a measure of the clarity of water. Silts and soils that are suspended within rivers and lakes cause high levels of turbidity, especially during storm and run-off events.