Precision Liquid Analysis for Drinking Water

Precision liquid analysis is an essential component of quality control for a number of industries. These include food and beverage production, chemical processing, petroleum refining, mineral processing, semiconductor production, and public utility water supply. Because many of these industries create products that directly affect the health and safety of their users, reliable analysis technology is critical. Perhaps in no industry is this more important than in the public potable water system. Following are some of the most common parameters monitored and controlled by liquid analyzer systems for ensuring drinking water quality.

pH and Alkalinity

Alkalinity is the ability of an aqueous solution to neutralize the acidic nature of another solution. Depending on the alkaline/acid base components, the neutralization process results in purified water along with some form of salt.

This process is particularly important in determining water pollution in a stream, river, or lake. Normally, stream motion neutralizes acidic pollutants. However, excessive pollution can overcome the purification ability of the stream, leaving an acidic imbalance. Pollution can come by direct insertion of pollutants (factory runoffs), rainwater runoffs through polluted ground, and rain droplets capturing airborne contaminants falling into bodies of water. A similar problem exists with wastewater and its neutralization at treatment plants.

The acidity or alkalinity of water is measured on a pH scale. pH values generally fall within the range of 1-15. A value of 7.0 represents a neutral solution. Solution values measuring less than 7.0 are acidic, while those above 7.0 are basic (or alkaline). Although the pH measurement of water is a strong indicator of water purity, it is not essential that the water measure precisely 7.0 on the pH scale. This is because the body regulates its own pH levels. However, pure drinking water should be in the range of 6.0 to 8.5 for surface water and 6.0 to 8.5 for groundwater systems.


Oxygen reduction potential (ORP) is a common measurement for the quality of water. The potential is the voltage level, and indicates the tendency of the molecules in the solution to attract electrons, or in other words, to be reduced. Technicians monitor ORP as part of a chlorination purification process. The amount of chlorination for a given volume is calculated and introduced, and then the effectiveness of the process is measured through ORP in millivolts. When the ORP rises above 665 mV for over 30 seconds, the survival rates of such pathogens as E. coli, Salmonella, and Listeria shrink to zero. Certain localities are considering introducing the 650 mV standard as part of their official standard health codes.

Contacting Conductivity

Electrolytic conductivity, also known as contacting conductivity, is another method for measuring water quality. This measurement is simple and inexpensive. It is performed by measuring the conductivity (the current for a given voltage) between two probes. This is similar to standard resistance measurements. Because conductivity testing is so easy, it is a common method of perform continual testing for water purification at facilities ranging from public supply departments to wastewater treatment plants. Typical drinking water should fall into the conductivity range of 5 to 50 mSiemens/m.

Dissolved Oxygen

Dissolved oxygen (DO), or the level of oxygen saturation, should be at full saturation levels for well-mixed bodies of water. These levels are about 10 mg/L at 15 oC. Insufficient oxygen saturation is often a sign of the presence of organic matter decomposition or nutrient pollution. The problem nutrients include an excess amount of nitrogen or phosphorus, which can stimulate algae growth. Low levels of DO indicate a problem with water quality.


Turbidity is the measure of cloudiness or haziness in a fluid. This haziness is rarely visible to the naked eye, and detection requires specific measurement instrumentation and sensors. These sensors allow analyst technicians to use the cloudiness factor to determine the percentage of particulates, either suspended or dissolved, in the solution. For this reason, it is another key test of water quality.

The particulates measured by turbidity come from several sources. One of these is growth of phytoplankton, which are microscopic members of the plankton community. Inorganic particles can be introduced by sediment from runoffs near construction, agricultural areas, and mining operations. These types of impurities can be difficult to treat, because the suspended solids can block the treatment of viruses and bacteria by chlorine or by UV radiation.

The most common measurement for turbidity involves shining a light through a volume of water, and measuring the reduction of light intensity. This is reported in units of JTU (Jackson turbidity unit), the inverse measure of the length of a water sample column, which completely obscures a candle flame.

For health standards, water must be tested with a calibrated nephelometer, which yields an output as an NTU (Nephelometric turbidity unit) value. (There is no direct conversion between JTU and NTU.) Individual states take the national EPA standard for turbidity limits and either use the adopted values or modify them to generate their own standards. These are generally in the range of 25 to 150 NTU.

Other standard measurements of water quality include toroidal conductivity, gaseous oxygen levels, chlorine content, and ozone content. Additional water quality tests include the following:

  • Taste and odor tests (focusing on geosmin, 2-Methylisoborneol (MIB), and similar compounds)
  • Dissolved salts and metals including sodium, calcium, potassium, manganese, and magnesium
  • Microorganisms such as Escherichia coli, Cryptosporidium, and Giardia lamblia
  • Dissolved organics, including colored dissolved organic matter (CDOM) and dissolved organic carb on (DOC)
  • Other contaminants, including radon, heavy metals, pharmaceuticals, and hormone analogs

Other Considerations

The ability to measure these quality parameters is enhanced by new sensor technologies. These include the use of automated equipment to replace manual testing processes. This makes it easier and faster for analysts to take consistent, high-reliability measurements. Wireless technology allows sensors to be placed in remote, low access areas, and still allow technicians to gather measurement data through a wireless link. Finally, analysis software provides standard methods to compile and analyze the data. This makes data analysis efficient and accurate, and provides the ability to create problem alerts. These alerts indicate problems to purification plant personnel through audio, visual, and text message alarms when measurements exceed prescribed limits.

These water quality analysis systems allow water authorities in all areas to control the quality of public drinking water. Similar systems use these parameters to make similar quality measurements in liquids of all kind. This allows related industries to improve the safety and health of their products as well as optimize quality.