Water Treatment Industry Commonly Used Units of Measurement And Their Meanings

Water treatment industry often use some general or unique units of measurement.

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The water treatment industry commonly used units of measurement and their meanings.

The water treatment industry often uses some general (such as length, weight, etc.) or unique (conductivity, turbidity, etc.) units of measurement to understand the meaning of these units of measure. Understanding the water treatment-related knowledge is very necessary.

Water treatment industry often use some general or unique units of measurement.


Length units

1 kilometer (Km) = 1000 meters
1 meter (m) = 1000 mm
1 millimeter (mm) = 1000 microns
1 micron (μm) = 1000 nanometers
1 nanometer (nm) = 10-9 meters
1 foot (ft) = 12 feet (inch)
1 inch (inch) = 25.4 millimeters (mm)


Unit of mass

1 ton (T) = 1000 kilograms (Kg)
1 kilogram (Kg) = 1000 grams (g)
1 gram (g) = 1000 milligrams (mg)
1 milligram (mg) = 1000 micrograms (μg)
1 microgram (μg) = 1000 nanograms (ng)
1 kilogram (Kg) = 2.205 pounds (lb)


Volume units

1 square (m3) = 1000 liters (L)
1 liter (L) = 1000 milliliters (ml)
1 U.S. gallon (G) = 3.785 liters (L)
Unit of solution concentration
1ppm=1mg/L (parts per million concentration)
1ppb=1μg/L (parts per billion concentration)
1ppt=1ng/L (parts per trillion concentration)


Unit of solution concentration

1ppm=1mg/L (parts per million concentration)
1ppb=1μg/L (parts per billion concentration)
1ppt=1ng/L (parts per trillion concentration)


Pressure unit

1 MPa = 106 Pascals (Pa)
1 MPa (MPa) = 10.2 kilogram force per square centimeter (Kg/cm2)
1 MPa (MPa) = 10 bar (bar)
1 bar (bar) = 14.5 pounds of force per square inch (psi)
1 kg force/cm2 (Kg/cm2) = 14.22 pounds force/square inch (psi)


Flow rate units

1 cubic meter per hour (m3/h) = 1000 liters per hour (L/h)
1 gallon per day (GPD) = 0.158 liters per hour (L/h)
1 gallon per minute (GPM) = 227 liters per hour (L/h)
Conductivity (μs/cm) & Resistivity (MΩ.cm)


Conductivity (μs/cm) & Resistivity (MΩ.cm)

Conductivity and resistivity values are reciprocal of each other and are one of the units of water purity measurement methods. Water contains anions and cations, ions for the conductive medium, by measuring the conductivity of water (resistivity value) can indicate the number of ions contained in the water, which indirectly reflects the level of water purity. Usually, we are accustomed to use the conductivity to reflect the purity of pure water, and the resistivity to reflect the purity of ultrapure water. Conductivity international unit for Siemens (Siemens), code for S, pure water conductivity value is very low, commonly used μS said. The international unit of resistance for the ohm, code for Ω, ultra-pure water resistance value is very large, commonly used MΩ said. The resistivity of water of extreme purity is 18.25MΩ.cm (0.055μs/cm ).


Total dissolved solids (TDS)

The unit is ppm to the total content of dissolved solids (inorganic and organic substances) in water (Total Dissolved Solids abbreviation). Usually used to measure the source water quality, the measurement principle is actually indirectly reflected by measuring the conductivity of the water’s TDS value. The more dissolved soluble solids in the water, the greater its TDS value, the greater the conductivity of the water, usually TDS value is about 1/2 of the conductivity test value, China’s Yangtze River basin urban tap water TDS value is usually 100-200ppm, the Yellow River basin tap water TDS value is usually 300-600ppm.

Note: TDS value and water salinity (also known as mineralization) are two different concepts. TDS value is usually greater than the salt content of water because TDS includes not only the amount of dissolved salt in the water, but also dissolved organic matter. Only in the premise that the water is very clean organic content is very low, only the TDS value can be used to approximate the salinity of water (or mineralization), in general, the TDS value, mineralization, salinity three in the water content is directly proportional to the relationship.


Turbidity (NTU)

Turbidity includes smaller organic and inorganic substances suspended in the water. This particulate matter can cause water turbidity and affect light emission. The turbidity unit is expressed as the degree to which the light beam can pass through the solution. The unit is NTU (Nephelometric Turbidity Unit). NTU is a scattering turbidity unit, indicating that the instrument measures the intensity of scattered light in a direction at an angle of 90° to the incident light. Turbidity can only indicate the number of suspended solids in the water and can not determine the content of dissolved impurities in the water. 1 litre of water containing 1mg of SiO2 (silica) degree of turbidity is 1 degree. The turbidity requirement of national standard drinking water is less than 5 degrees; the turbidity of supplementary water for circulating cooling water treatment is 2~5 degrees; the turbidity of incoming water (raw water) for desalination water treatment should be less than 3 degrees; the turbidity of incoming water for reverse osmosis should be less than 1 degree.



The hardness of water refers to the content of dissolved calcium and magnesium salts in water (of which calcium salts account for about 85%, magnesium salts 10-15%, other metal salts 1-3%), mainly refers to the content of Ca2+, Mg2+ ions in water, Ca2+/Mg2+ in water mainly from the dissolution of calcium and magnesium salts in rocks (CaCO3/MgCO3), when the content of CO2 gas in water is more the dissolution progress will be greatly accelerated. Hardness is divided into temporary hardness (carbonate hardness can be removed by heating and precipitation) and permanent hardness (non-carbonate hardness, which cannot be removed by heating and boiling). The total sum of the two is called total hardness. The international unit of water hardness is German hardness, 1 liter of water containing 10mg of CaO (calcium oxide) content is 1 German hardness, hardness greater than 8 degrees (equivalent to 200ppm) of water for hard water, China’s national standard for drinking water provides that the total hardness index shall not be greater than 450ppm.


PH value

PH value indicates the negative logarithmic value of the H+ concentration in water, also known as the hydrogen ion index. PH value can indicate the magnitude of change in the solution acidity, alkalinity of the magnitude of change.

Strongly acidic aqueous solution: PH<5.0
Weakly acidic aqueous solution: PH=5.0~6.5
Neutral aqueous solution: PH=6.5~8.0
Weakly alkaline aqueous solution: PH=8.0~10
Strongly alkaline aqueous solution: PH>10

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John Lau.

John Lau, oversea project manager, an engineering graduate with expertise in optimizing beverage production equipment during his university studies, is now at the helm of global projects in the industry. Committed to educating clients on the benefits of customized equipment solutions that notably boost operational efficiency, Lau views this specialization in tailoring bottling machines as a key facet of his professional commitment.

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