TDS (Total Soluble Solids) is a measure of the total amount of all ions in water, usually expressed in ppm . The conductivity of the solution is equal to the sum of the conductivity of the various ions in the solution.
In pure water who manufactures, conductivity can also be used to indirectly represent TDS .
The empirical formula is: half the conductivity in microsiemens is approximately equal to TDS ( ppm )
Sometimes TDS is also represented by other salts , such as CaCO3 ( coefficient is 0.66)
The conversion factor of TDS and conductivity can be adjusted between 0.4 and 1.0 to correspond to different kinds of electrolyte solutions.
Conductivity
Conductivity is the ability of a substance to carry a current, as opposed to the resistance value, in units of Siemens/cm .
Water hardness
The hardness of water refers to the concentration of calcium and magnesium ions in water. The hardness is in ppm , and 1 ppm represents the calcium carbonate content of 1 mg / L ( mg/L ).
Water hardness unit conversion
Hardness unit ppm German hardness       French hardness         British hardness
1ppm = 1.000ppm 0.0560 0.1 0.0702
1 German hardness = 17.847ppm 1 1.7847 1.2521
1 French hardness = 10.000ppm 0.5603 1 0.7015
1 British hardness = 14.286ppm 0.7987 1.4285 1
Conductivity and water hardness
The conductivity of the aqueous solution is directly proportional to the concentration of dissolved solids, and the higher the concentration of solids, the greater the conductivity. The relationship between the conductivity and the dissolved solids concentration is approximately expressed as: 1.4 μS/cm = 1 ppm or 2 μS/cm = 1 ppm (per million units of CaCO3 ). The total hardness value of water can be obtained indirectly by using a conductivity meter or a total solids dissolution meter. As described above, for the convenience of approximate conversion, 1 μs/cm conductivity = 0.5 ppm hardness.
But need to pay attention to: ( 1 ) indirectly measure the hardness of water with conductivity, the theoretical error is about 20-30ppm. ( 2 ) The conductivity of the solution determines the movement of the molecule, and the temperature affects the movement of the molecule. In order to compare the measurement results, the test temperature is generally set to
Soft and hard water
Water is divided into soft water and hard water. Any water that does not contain or contain a small amount of calcium or magnesium ions is called soft water, and vice versa. The hardness component of water, if it is caused by sodium bicarbonate or magnesium bicarbonate, is temporary hard water (boiled temporary hard water, decomposed sodium bicarbonate, precipitated insoluble carbonate, and water changes from hard water to soft water) If it is caused by sulfate or chloride containing calcium or magnesium, it is permanent hard water. According to the total hardness value of water, the total hardness is 0-30ppm, which is called soft water. The total hardness is 60ppm or more, which is called hard water. The high-quality drinking water does not exceed 25ppm . The high-quality soft water has a total hardness of 10ppm or less. In natural water, away from the city, unpolluted rainwater and snowwater are soft water; spring water, stream water, river water, and reservoir water are mostly temporary hard water, and some groundwater is high hardness water.
The conversions for common units of water hardness conversion are :
1mmol / L (1 / 2Ca2 + , 1 / 2Mg2 +) = 50 ppm ( in terms CaC03)
1mmol/L (1/2Ca2+ , 1/2Mg2+)=2.92 grain/gallon ( grain / gallon )
lgrain / gallon (grains / gallon) = 17.lppm (in terms CaC03)
Lkg=2.2pounds ( £ )
1ppm=1mg/L