Gravimetrically method is more reliable because it includes both conductive and non conductive particles. On the other hand EC meter gives the value of conductive particles only and exclude non conductive material.

For further detail link is given below

http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502015000400008

By using EC method you measure only the materials that conduct electricity

But G you measure each material present

This means the second is more accurate

Both answers above are appropriate. EC will not measure the dissolved organics. For a given water source, you can in most instances correlate TDS. and EC, and then run EC to help save on costs and time. If you sample stormwater, the potential for organics may increase, so running TDS is best for accuracy. If sampling wastewater with more potential for dissolved organics or blackwater from extensive wetland sources, TDS is going to be best. By running both, and with experience and keeping track of the type of water, the water source and conditions of sampling, you may find that EC will produce acceptable results for some of your needs. If for use in court testimony, TDS will measurte both inorganic and organic dissolved solids, while EC measures the electrical current passing through dissolved inorganics. As long as you know the difference between them, develop correlation when needed, and present the best information you have available and include or disclose level of uncertainty, that is about all that can be expected. If you TDS and only have EC, you may be able to resample and run some correlations after the fact if the water sources have not significantly changed, but also disclose this in methods if there is high correlation and then conversion of EC to estimated TDS. Any TDS calculated from correlated EC values should probably be reported as estimated TDS.

Forgot to mention, standard methods book for analysis of water and wastewater is a helpful reference. Also running some standard concentrations will help check on instrument performance, methods, etc. when running samples.

I think, the results of EC-meter should be interpreted separately. Results obtained through EC- meter can't be called Total dissolved solids. It will may be more appropriate to call it total dissolved ions.

Agreed with Khaled Muftah answer

Maybe the answer relies on the meaning of reliability for what. The purpose of conducting analysis is to get information from the real world sample or population. Different method has its principle and scope and gets different information. So just define yourself the information ahead before your analysis.EC and G are different both in principle and the information it got.

Yes Bo Zheng, methods of measurement are different but analytical results of both are expressed as " Total dissolved solids mg/L".

I think it may be clear now.

The answer is clear: only the gravimetrically determined method provides reliable results. The EC/TDS method is a calculation using a conversion factor which ranges from 0.25 to 1.34 [µS/cm and mg/L] . If – and only if – you predetermined the conversion factor for a given site THEN you can use the EC/TDS ratio and it will also be reliable. Please see my paper

Hubert, E. & Wolkersdorfer, C. (2015): Establishing a conversion factor between electrical conductivity and total dissolved solids in South African mine waters. – Water SA, 41(4):490-500, 6 fig., 8 tab.; doi:10.4314/wsa.v41i4.08.

for details and more references.

So, to answer the last part of your question: determine the EC (at 25 °C = κ) / TDS ratio for several samples of your site(s) using the gravimetrical method (ensure you calibrate your EC meter) and then use this factor f to calculate TDS as follows:

TDS [mg/L] = f × κ [µS/cm]

In my experience the EC derived measure is more precise, while the gravimetric method is more accurate. Selecting which is better is dependent on the goal of the study.

the Gravimetric method is the most reliable and sensitive method when determining Total Dissolved Solids .Using an EC meter you can input a conversion factor for TDS so that the meter can calculate the TDS based on the EC ...usually the factor is 0.55-0.70 .Since the Gravimetric method is time consuming and also is not very applicable when you are analysing a lot of samples ,some analysts just input a conversion factor usually 0.64 and get the TDS from the EC ,but it is important to state that it is an estimated value . You could use Gravimetric method once for your batch of samples and from that get the actual factors of TDS/EC of the different samples and proceed to use the EC meter with those factors.This equation can also help you check the correctness of your analyses

Total dissolved solids = 0.6 (alkalinity*#(2)) + Na+ + K+ + Ca2+ + Mg2+ + Cl−+ SO4 + SiO3 + NO3− + F−

but will only work if you have analysed for these particular cations and anions

Thank you Moses Souta for such details.

Regards

I want to confirm what many have already said, the gravimetric method is more reliable for TDS.

In most cases the results of the gravimetric method are higher than the conductivity measured species. Conductivity is directly associated with dissolved ionic solids, whereas, the weighed material combines all the constituents including non ionic materials like the organics. Thus, the difference between the two results is indicative of the organic soluble matter... Good luck.

Electrical conductivity just measure approximate total dissolved solids. Gravimetric analysis is better option.

Well,

the answers proceeded by

Virendra Kumar Saxena , William F. Hansen are recommended.

Sincerely

I appreciate and recommend the following statements:

Dr. Christian – “gravimetrically determined method provides reliable results. The EC/TDS method is a calculation using a conversion factor”.

Dr. Moses – “Since the Gravimetric method is time consuming and also is not very applicable when you are analysing a lot of samples ,some analysts just input a conversion factor usually 0.64 and get the TDS from the EC, but it is important to state that it is an estimated value . You could use Gravimetric method once for your batch of samples and from that get the actual factors of TDS/EC of the different samples and proceed to use the EC meter with those factors”

Many thanks to Moses Souta and Christian Wolkersdorfer for such elaborate explanations.

I also go for gravimetrically determed value since it is normally used to calibrate the meters.

https://www.alliancecalibration.com/blog/what-is-the-difference-between-conductivity-and-tds