Water By Elena Tezak — Date 08.26.2016

Probing water: the relevance of water quality

Quality indicators vary according to what you want to know. Sometimes it's about ecology. Sometimes it's about safe drinking water.

Water quality describes chemical, physical, biological, and radiological properties in water and is the measure of water condition in relation to its purpose. The purpose can be to establish a healthy environment, or to be used by humans—the parameters for indicating its quality vary accordingly. The most common reasons to measure water quality are to monitor the condition of an eco system and to determine the safety for human contact, both for natural water bodies and drinking water.

In developed countries we often equal tap water with drinking water, though this is not necessarily the case everywhere. Therefore we won’t get into the specifics of regulations, but instead try to illuminate how various the aspects of water quality are with examples of how they can be measured.

The factors that are measured are distinguished into the following categories: Microorganisms (viruses, bacteria, and protozoa), inorganic contaminants (salts, metals, gas), organic chemicals (industrial and agricultural effluents, pharmaceuticals), and radionuclides. Each of these categories contains a number of substances, whose occurrence is lawfully regulated, and their measuring requires different techniques.

The water Probe

One method of measuring the total occurrence of various substances is testing the electric conductivity of a water probe. Pure water consists solely of hydrogen and oxygen. Both elements are not conductive. Yet, certain other substances, like minerals, salts, and metals, are. Their concentration in a water probe therefore can be determined through the water’s conductivity. They are referred to as the amount of total dissolved solids (TDS), indicated as milligrams per liter (mg/L), or respectively parts per million (ppm).

Bacteriological water analysis can be carried out through plate count, combined with membrane filtration: After filtering a water probe, the membrane is placed in a nutrient solution, where the bacteria will breed. After a set time, the cultures are counted. Since all surveys are based on a comparatively tiny probe, the results are based on statistic principles.

Neutral pH

Further factors that require chemical analysis are alkalinity and pH: While alkalinity describes the water’s ability to neutralize an acid, pH is the actual value of the water’s acidity or basicity. By definition, pH is the negative decimal logarithm of the reciprocal of the hydrogen ion activity. It is commonly measured on a scale from 0-14, whereas the the value 7 means that a substance is neither acid, nor basic, thus it is defined as neutral. For a healthy environment and if used by humans, water should have a neutral or slightly basic pH.

Another quite interesting measure is the water’s turbidity, or haze. The Formazin Turbidity Unit (FTU) is defined through evaluating the scattering of incident light on a water probe. The haze is caused by fine parts of inorganic and organic matter, microscopic organisms, as well as algae, plankton, clay, and silt in natural water bodies. High intensity of scattered light equals high turbidity.


This is just a small fraction of what it means to test for water quality. Responsible for quality testing and documenting the results are the distributing water suppliers, who are obliged by law to guarantee the water quality from the plant up until it reaches the piping of the private or industrial end user. They either have in-house laboratories, or work with certified laboratories.

For further information, you can look up the website of your local water supply company to read more about the water regulations in your state, how they are ensured, and the origin of your tap water.

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