Measuring Total Dissolved Solids (TDS) in water

Date: 18/12/19 | In: Water Quality

The measurement of Total Dissolved Solids (TDS) in water is a key task for every water company, as well as any business producing trade effluent. Understanding the cause and effect of TDS through robust monitoring is critical for improving processes and efficiencies and achieving regulatory compliance.

But what is TDS and what is the most effective way of measuring it?

What are Total Dissolved Solids (TDS)?

Total dissolved solids is a combination of inorganic and organic substances that are dissolved in water, including wastewater. These solids can be salts, minerals, metals, cations or anions. Common inorganic salts that are found as dissolved solids in water include calcium, potassium, magnesium, sodium, sulphates and chlorides. Water may pick up metals such as lead or copper whilst travelling through distribution pipes. Pesticides, fertilisers, leaves and even road salt used in winter months can all contribute to TDS levels.

TDS is usually measured in milligrams per unit volume of water (mg/L). TDS can also be referred to as parts per million (ppm).

What’s the most effective way of measuring TDS in water?

The amount and composition of TDS in water is linked to the electrical conductivity of the water. As such, of the most effective ways of measuring TDS in water is by measuring the conductivity of the water itself.

Our TDS meter is designed to measure conductivity in water from 0 to 2,000,000 µS/cm (range selectable). There is a choice of a standard graphite sensor or a more sophisticated toroidal sensor. For exceptional applications, we also provide a stainless steel sensor for high temperature, high pressure conductivity measurement applications.

When connected to the ORAKEL controller, it turns into one of the best water conductivity meters on the market. The ORAKEL controller provides a variety of communication protocols, on screen display and numerous control options.

How does the TDS meter and ORAKEL controller work?

The TDS meter uses electrodes to encourage microorganisms to grow on the surface of the probe before they grow on the surface of the pipe. The biological activity of the biofilm creates a signal. The controller collects and monitors that signal continually. An increasing trend in the signal indicates the onset of biofilm activity on the probe.

The controller can then take corrective action such as increasing or decreasing the biocide levels, triggering email or text alarms and data logging. This can all be done automatically with the right configuration.

Total Dissolved Solids (TDS) and salinity are both measured with conductivity sensors, and the ORAKEL controllers can provide outputs and on screen displays of calculated TDS and salinity readings from the conductivity sensors. ORAKEL controllers come with standard user adjustable, factors for calculating TDS and salinity.

Applications: choosing the ideal sensor


Our light industrial conductivity sensor utilises Graphite technology. The durable epoxy body construction provides a rugged and dependable sensor for potable water and clean water. Mount them in-line, in a pipe “T” fitting, or submerse them into a tank. For many applications, the epoxy body conductivity sensors are the lowest cost, most reliable conductivity sensor to use, especially for process applications. Rugged epoxy bodies make the sensors virtually unbreakable. These are an excellent choice to use as standard online conductivity electrodes in the water and related industries.


The toroidal inductive conductivity sensors feature a wide measurement range and dependable toroidal technology over the range 0-2,000,000 µS/cm. Resistant to corrosion, coatings and fouling common to contacting conductivity sensors, this probe is designed for a trouble free and long service life. Noryl is the standard material of construction and has a wide solvent tolerance and temperature stability to 105ºC.  All models can be submersed by utilising the 3/4” MNPT threads on the sensor or installed in 2” NPT tees for in-line deployment. A temperature sensor is built into the conductivity sensor for automatic temperature compensation.

To find out more about measuring TDS or how our range of conductivity meters could enable you to measure TDS in water in your organisation, please contact us on 01282 449124 or email: