Http://www.molecular-beacons.org/download/lerga,aca08%28610%29105.pdf

http://www.ntsensors.com/durent_eng.html

For very accurate meassurements ICP-OES or FAAS spectroscopy. There is also ISE (Ion Selective Electrodes) but I have found that they are very expensive for what they are and do not last.

If you don't have these analytical instruments available then the complexometric EDTA titration with eriochrome black-T indicator.

HACH water testing has a field kit available if you just want ranges of concentrations.

Thank you very much for your replies.

The titration with EDTA is the most true method as it defines the parameter hardness. There is no need to use more advanced methods if the analytic question is just to find the hardness of the water.

Thanks a lot Henrik.

Please receive the paper. I hope having your help.

Complexometric method . This volumetric, in which NA2EDTA is main and Eriochrome Black T indicator is used This is quick and reliable. Detail of the method is available in USGS.

Thank you very much for your answer

Thanks Yanick you are agreed with my answer.

As per APHA methods

EDTA Titration method is the best method i feel to fount total hardness and Calcium and magnesium

EDTA titration method is the best.

For the determination of total hardness, we have used EDTA Volumetric  method, and our results found to be reliable. work published in repute journal and well cited. This method is economical viable and quick and without any much technology. For more accuracy standardisation and calibration may be useful.