pH, EC, TDS, Salinity, and Temperature – These parameters can be determined by the multiparameter tester or pocket tester, very simple device and highly suitable for site work.
This type of device is available from Hach, Eutech, or HANNA . Almost all good. I am using a model of Eutech (Approx. cost INR 40,000), the specification of which is attached for your reading. But, I suggest you to compare the specification with other makes for selection.
For a very wide range of physical and chemical parameters to be determined in wastewaters and drinking waters I suggest you a portable spectrophotometer. I use the model Photolab S12 made by WTW, it is very much reliable but very simple in operation as well. Moreover, its small size and small test-kits (tubes) make it very suitable for on-site application. See in the attached brochure how many parameters you can check if use the model S12 (or other model presented in brochure). I'm sure you can find supliers of WTW equipments nearby.
YSI Pro DSS multiparameter instrument is excellent instrument for field measurements of water quality. I have it and use since a few years.
However, before to purchase the instrument I need to inform you that with the Pro DSS you can not measure Phosphates, Nitrites and COD, and also in slightly salt waters you can not also measure Ammonium, Chloride and nitrates (these 3 last parameters can be measured with Pro DSS only in fresh water).
You can also buy the instrument if you are still interested:
Xylem Analytics
Surface/Ocean & Coastal Waters Sales Manager Europe
Various type of Multiparameter kits are available in the market. But I would suggest instead of purchasing one instrument for most of the water quality parameter, you should purchase two three hand held instruments available from Eutech, WTW, HACH etc.
Eutech is comparably less expensive among all. We are using Eutech from past many years and very satisfied. We do also have YSI but frankly speaking, I am not very much satisfied with its performance. Moreover, it is comparably very costly.
You can purchase one pocket size meter for For pH, EC, and Temperature. One for ions and one for DO. I give preference to HACK (LDO probe and meter) for DO and BOD.