? who knows how / where ( location KOH SAMUI ) to

check watersamples from well / townsupply

regarding chemical and biological quality.

- by a company / institute / ?hospital?

- by a affordable test set / equipment

What are you thinkind is wrong with your water? If you are worried about certain VOC's and many heavy metals, you aren't going to be able to pick up a test kit to check for these things. For bacteria, you can sometimes find agencies that will send you a container to take a sample and then you have to send it back and they will incubate a sample to look for such things as fecal coliform or e. coli.

There must be some environmental consultancy firms there that might be able to help you? That or check with the local university. They may have an environmental lab to run certain tests.

You could contact the Ministry of Public Health office and ask for advice. They may be able to help as one of their functions is to check the water quality at water bottling factories.