What are the possible ways or technologies available to implement my idea?
My idea is to invent a water purity tester.
Already, some water purity testers are available. In addition to that, I want to add some more features to it.
Very vague. Are you considering testing for chemical purity or for safety for human consumption as per US EPA specifications?
Any chemical more than 98% pure can be labelled as ‘Chemically Pure’ (CP)as per standards. By this count, untreated sewage can be labelled Water (CP), since it is >98% water.
The US EPA standards for drinking water can be seen here :
Tough job if you want to develop a test system for this. Please check out the details and revert with what you want to do.
If you want to do TDS alone a hand held conductivity meter may do the job.