salinity is measured by electrical conductivity (EC) using a conductivity bridge. The total salt content of a soil can be estimated from this measurement. A more precise method involves evaporation of the aqueous extract and weighing the residue (total dissolved solids, TDS).

EC(dS/m)*640=TDS(mg/l) (Accuracy -+10)

in water the TSS is a well-mixed sample is filtered through a weighed standard glass-fiber filteand the residue retained on the filter is dried to a constant weight at 103 to 105°C. The increase in weight of the filter represents the total suspended solids.  To obtain an estimate of total suspended solids, calculate the difference between total dissolved solids and total solids.

while ‘Dissolved solids’’ is the portion of solids that passes through a filter of 2.0 µm (or smaller) nominal pore size under specified conditions. ‘‘Suspended solids’’ is the portion retained on the filter.

Sum concentrations (in milligrams per liter) of constituents to calculate the total dissolved solids are as follows: Total dissolved solids = 0.6 (alkalinity*#(2)) + Na+ + K+ + Ca2+ + Mg2+ + Cl−+ SO42− + SiO32− + NO3− + F−

Both the anion and cation sums should be 1/100 of the measured EC value. If either of the two sums does not meet this criterion, that sum is suspect; reanalyze the sample. The acceptable criteria are as follows: 100 × anion (or cation) sum, meq/L = (0.9–1.1) EC

If the ratio of calculated TDS to conductivity falls below 0.55, the lower ion sum is suspect; reanalyze it. If the ratio is above 0.7, the higher ion sum is suspect; reanalyze it. If reanalysis causes no change in the lower ion sum, an unmeasured constituent, such as ammonia or nitrite, may be present at a significant concentration. If poorly dissociated calcium and sulfate ions are present, the TDS may be as high as 0.8 times the EC. The acceptable criterion is as follows: calculated TDS/conductivity = 0.55–0.7

The acceptable criteria for this ratio are from 0.55 to 0.7. If the ratio of TDS to EC is outside these limits, measured TDS or measured conductivity is suspect; reanalyze.

There is high correlation between electrical conductivity (EC) and total dissolved solids (TSS). The more salts dissolved in soil solution, the higher is the value of electrical conductivity in soil. A general relationship has often been applied to determine TSS from electical conductivity i.e., TSS (mg/l) = ECe x 640. ECe represents electrical conductivity of saturation extract.

The mentioned book is one of the most widely used book for elemental analysis and measuring nutrient availability in soils and, perhaps you can get the mentioned book chapter from the library of your university.

Cheers!!!!

There is invariably a positive relation between TSS and EC . I agree with response from Sovan . However , this issue , we have debated  number of times on the same platform 

salinity is measured by electrical conductivity (EC) using a conductivity bridge. The total salt content of a soil can be estimated from this measurement. A more precise method involves evaporation of the aqueous extract and weighing the residue (total dissolved solids, TDS).

EC(dS/m)*640=TDS(mg/l) (Accuracy -+10)

in water the TSS is a well-mixed sample is filtered through a weighed standard glass-fiber filteand the residue retained on the filter is dried to a constant weight at 103 to 105°C. The increase in weight of the filter represents the total suspended solids.  To obtain an estimate of total suspended solids, calculate the difference between total dissolved solids and total solids.

while ‘Dissolved solids’’ is the portion of solids that passes through a filter of 2.0 µm (or smaller) nominal pore size under specified conditions. ‘‘Suspended solids’’ is the portion retained on the filter.

Sum concentrations (in milligrams per liter) of constituents to calculate the total dissolved solids are as follows: Total dissolved solids = 0.6 (alkalinity*#(2)) + Na+ + K+ + Ca2+ + Mg2+ + Cl−+ SO42− + SiO32− + NO3− + F−

Both the anion and cation sums should be 1/100 of the measured EC value. If either of the two sums does not meet this criterion, that sum is suspect; reanalyze the sample. The acceptable criteria are as follows: 100 × anion (or cation) sum, meq/L = (0.9–1.1) EC

If the ratio of calculated TDS to conductivity falls below 0.55, the lower ion sum is suspect; reanalyze it. If the ratio is above 0.7, the higher ion sum is suspect; reanalyze it. If reanalysis causes no change in the lower ion sum, an unmeasured constituent, such as ammonia or nitrite, may be present at a significant concentration. If poorly dissociated calcium and sulfate ions are present, the TDS may be as high as 0.8 times the EC. The acceptable criterion is as follows: calculated TDS/conductivity = 0.55–0.7

The acceptable criteria for this ratio are from 0.55 to 0.7. If the ratio of TDS to EC is outside these limits, measured TDS or measured conductivity is suspect; reanalyze.

Electrical conductivity and Total Dissolved Solids are directly related. TDS/ EC is approximately 0.6 to 0.7. This factor varies with water type and presence of chemical constituents in it.

The relation between TDS and conductance can vary between water sources some. Here in Iowa (US) I have found this factor to be close to 0.6 in most circumstances.

Approximately, EC=0.6-0.7xTDS

I think , Christopher as raised a good  point , we need such relation to be adjusted  . , depending upon the ionic  composition of the water , to arrive at any such relation , however such relations  could act as line information , no doubt about it ...

It may be helpful to read the following paper

https://www.researchgate.net/publication/259641651_Relationship_between_chloride_concentration_and_electrical_conductivity_in_groundwater_and_its_estimation_from_vertical_electrical_soundings_VESs_in_Guasave_Sinaloa_Mexico?ev=prf_pub

Article Relationship between chloride concentration and electrical c...

Because almost all the conductivity is accounted for by the dissolved ions, there is a direct proportionality between EC and TDS: TDS=EC x f,  where This conversion factor f allows the estimation of TDS from a precisely measured EC.

TDS is expressed in mg/L and EC is the electrical conductivity in microsiemens per cm. The correlation factor f varies between 0.55 and 0.8

At lower concentrations, the relation between concentration and EC for single electrolyte solutions is linear and flattens off for higher ones because the ionic mobility decreases with increasing concentration due to interferences and interactions between the ions.

TDS denotes all dissolved solids - usually mineral salts that are dissolved in water. There is a close relation between TDS and the electrical conductivity. Conductivity is direct function of salt concentration. More the salts dissolved in the water, the higher is the electric conductivity. To equate, TDS=EC x f, where  f is the conversion factor

Can we say , there can not be any universal empirical relation between TDS and EC, despite the fact that there is direct relation between the two parameters..

A correlation can only  exist if the the dissolved solids include only ionic compounds and there are no soluble mineral acids. Any non-ionic solids, like sugars, will give no conductivity signal. Any strong acids (HCl, HNO3, H3PO4 [not officially "strong] ) will give a very large signal despite not being dissolved solids. Different ions make different contributions to the conductivity.So you can use conductivity for TDS only if the solids composition of your samples is fairly well fixed. So you can't use the same correlation for sea water and for sewage.

Well said Roger, some valid points...

Thank all! Your information is very useful.

Thanks guys. Here in Ghana, our applied EPA limit for liquid waste in the relation of TDS/EC is found to be 0.67 which corresponds to the acceptable range of 0.55-0.7.

There the significant +ve correlation between Ec and TDS

Ec (dS m-1) = TDS(ppm)/640

The value 640 is not constant but depends on chemical composition of water or the the concentration of main ions in water.

We found the correlation factor for 45 natural waters and mine waters to range between 0.25 and 1.34, with a median of 0.85, for South Africa. The factors are site specific and must be determined case by case. No “general” fits all factor can be used.

Article Establishing a conversion factor between electrical conducti...

Total concentration of soluble salts is the main criterion for assessing the quality of irrigation water. Two methods are commonly used for determination of salt concentration.

The salinity of irrigation water is sometimes reported as total dissolved solids (TDS) in mg/L. However, this method is accurate in the case of irrigation water free of bicarbonates only.

A better way of expressing salinity is through electrical conductivity (EC) expressed in decisiemens/metre (dS/m) or millisiemens/m (mS/m). EC is a much more useful measurement than TDS because it can be made instantaneously and easily by farm managers in the field. Salts that are dissolved in water conduct electricity, and, therefore, the salt content in the water is directly related to EC.

It has been established that electrical conductivity of irrigation water (ECiw) is almost proportional to the amount of salts present in it. The total dissolved salts (TDS) in water can be estimated by its relation to electrical conductivity (ECiw in dS/m) given as:

when ECw is less than 5 dS/m:

TDS (mg/L) = 640 x ECw (dS/m),

TDS(%) = 0.64X x ECw (dS/m)

1dS./m= 640ppm = 640mg/L= 0.64g/L= 0.064%

When ECw is greater than 5 dS/m:

TDS (mg/L) = 800 x ECw (dS/m)

However, caution is advised in such conversions because conversion factors depend both on the salinity level and composition of the water. Sulphate salts do not conduct electricity in the same way as other types of salts. Therefore, if water contains large quantities of sulphate salts, the conversion factors must be adjusted upwards.

As I pointed out in my answer above, the recommendation of C George Thomas only works after one conducted a site specific determination of the EC / TDS ratio, as the ratio can range in a very large range. It is not possible to use predefined conversion factors without evaluating their validity.

Also the units dS/m or mS/m are just examples. Most instruments measure only mS/cm or µS/cm. It needs a lot of care to ensure the correct unit is recorded when using field or lab instruments. It would be more accurate to say that the EC is measured in “electric conductance” [S] per “length” [m].

Thank you Christian Wolkersdorfer for your enlightening comment. I agree with your observations.

TDS = 0.67*(EC)

If it is seawater what will be conversion factor to find TDS in ppm

The dominate ions in sea wateer are Na and Cl both of them are very active since Cl not contributes in ion pairig and the contribution of Na in ion pairing is very low for this reason the value is mor than 640 may reaches to 670.

Thank you professor Dr Akram

Thank you for discussion

the relation between EC and TDS also depends on water family the reange of EC

TDS = 0.66 (E.C.)

Dear Muhammad Shoukat Hussain it is a very good result

This should be considered as empirical relationship and thus, the factor may not be always same as described, but varies in place to place due variation in composition of TDS.